diff --git a/build.gradle b/build.gradle
index 87254a3a..8102a907 100644
--- a/build.gradle
+++ b/build.gradle
@@ -12,6 +12,7 @@ repositories {
 dependencies {
     testImplementation platform('org.junit:junit-bom:5.9.1')
     testImplementation('org.junit.jupiter:junit-jupiter')
+    testImplementation('org.assertj:assertj-core:3.24.2')
 }
 
 test {
diff --git a/src/main/java/Calc.java b/src/main/java/Calc.java
new file mode 100644
index 00000000..381c6173
--- /dev/null
+++ b/src/main/java/Calc.java
@@ -0,0 +1,24 @@
+public class Calc {
+    public int add(int a, int b) {
+        int res = a + b;
+        return res;
+    }
+
+    public int minus(int a, int b) {
+        int res = a - b;
+        return res;
+    }
+
+    public int times(int a, int b) {
+        int res = a * b;
+        return res;
+    }
+
+    public int divide(int a, int b) {
+        if (b == 0) {
+            throw new IllegalArgumentException("0 으로 나눌 수 없습니다.");
+        }
+        int res = a / b;
+        return res;
+    }
+}
\ No newline at end of file
diff --git a/src/main/java/StringCalc.java b/src/main/java/StringCalc.java
new file mode 100644
index 00000000..55af9585
--- /dev/null
+++ b/src/main/java/StringCalc.java
@@ -0,0 +1,78 @@
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
+
+public class StringCalc {
+
+    private static final String DEFAULT_DELIMITERS = "[,:]";
+
+    public int add(String text) {
+        if (isNullOrEmpty(text)) {
+            return 0;
+        }
+
+        DelimiterInfo delimiterInfo = parseDelimiterInfo(text);
+        String[] numbersAsString = splitByDelimiter(delimiterInfo.textToParse, delimiterInfo.delimiter);
+        
+        return calculateSum(numbersAsString);
+    }
+
+    private boolean isNullOrEmpty(String text) {
+        return text == null || text.isEmpty();
+    }
+
+    private DelimiterInfo parseDelimiterInfo(String text) {
+        Pattern customDelimiterPattern = Pattern.compile("//(.)\n(.*)");
+        Matcher matcher = customDelimiterPattern.matcher(text);
+
+        if (matcher.find()) {
+            String customDelimiter = Pattern.quote(matcher.group(1));
+            String actualTextToParse = matcher.group(2);
+            // 커스텀 구분자와 기본 구분자를 모두 포함
+            String combinedDelimiters = DEFAULT_DELIMITERS + "|" + customDelimiter;
+            return new DelimiterInfo(combinedDelimiters, actualTextToParse);
+        }
+
+        return new DelimiterInfo(DEFAULT_DELIMITERS, text);
+    }
+
+    private String[] splitByDelimiter(String text, String delimiter) {
+        return text.split(delimiter);
+    }
+
+    private int calculateSum(String[] numbersAsString) {
+        int sum = 0;
+        for (String numStr : numbersAsString) {
+            if (numStr.isEmpty()) {
+                continue;
+            }
+            sum += parseAndValidateNumber(numStr);
+        }
+        return sum;
+    }
+
+    private int parseAndValidateNumber(String numStr) {
+        try {
+            int number = Integer.parseInt(numStr);
+            validateNumber(number);
+            return number;
+        } catch (NumberFormatException e) {
+            throw new RuntimeException("숫자 이외의 값이 포함되어 있습니다.");
+        }
+    }
+
+    private void validateNumber(int number) {
+        if (number < 0) {
+            throw new RuntimeException("음수는 입력할 수 없습니다.");
+        }
+    }
+
+    private static class DelimiterInfo {
+        final String delimiter;
+        final String textToParse;
+
+        DelimiterInfo(String delimiter, String textToParse) {
+            this.delimiter = delimiter;
+            this.textToParse = textToParse;
+        }
+    }
+}
\ No newline at end of file
diff --git a/src/test/java/CalcTest.java b/src/test/java/CalcTest.java
new file mode 100644
index 00000000..f19a6662
--- /dev/null
+++ b/src/test/java/CalcTest.java
@@ -0,0 +1,60 @@
+
+import org.junit.jupiter.api.DisplayName;
+import org.junit.jupiter.api.Test;
+import static org.assertj.core.api.Assertions.*;
+
+@DisplayName("계산기 작동 테스트")
+public class CalcTest {
+    private final Calc calc = new Calc();
+
+    @Test
+    @DisplayName("더하기 테스트")
+    void add() {
+        final var a = 1;
+        final var b = 2;
+        final var actual = calc.add(a, b);
+        
+        assertThat(actual).isEqualTo(3);
+    }
+
+    @Test
+    @DisplayName("빼기 테스트")
+    void minus() {
+        final var a = 3;
+        final var b = 1;
+        final var actual = calc.minus(a, b);
+        
+        assertThat(actual).isEqualTo(2);
+    }
+
+    @Test
+    @DisplayName("곱하기 테스트")
+    void times() {
+        final var a = 2;
+        final var b = 3;
+        final var actual = calc.times(a, b);
+        
+        assertThat(actual).isEqualTo(6);
+    }
+
+    @Test
+    @DisplayName("나누기 테스트")
+    void divide() {
+        final var a = 10;
+        final var b = 5;
+        final var actual = calc.divide(a, b);
+        
+        assertThat(actual).isEqualTo(2);
+    }
+
+    @Test
+    @DisplayName("0으로 나누기 예외 테스트")
+    void divideByZeroThrowsException() {
+        final var a = 10;
+        final var b = 0;
+        
+        assertThatThrownBy(() -> calc.divide(a, b))
+            .isInstanceOf(IllegalArgumentException.class)
+            .hasMessage("0 으로 나눌 수 없습니다.");
+    }
+}
\ No newline at end of file
diff --git a/src/test/java/StringCalcTest.java b/src/test/java/StringCalcTest.java
new file mode 100644
index 00000000..9cdb0195
--- /dev/null
+++ b/src/test/java/StringCalcTest.java
@@ -0,0 +1,92 @@
+
+import org.junit.jupiter.api.DisplayName;
+import org.junit.jupiter.api.Test;
+import static org.assertj.core.api.Assertions.*;
+
+@DisplayName("문자열 계산기 테스트")
+class StringCalcTest {
+    private final StringCalc stringCalc = new StringCalc();
+
+    @Test
+    @DisplayName("쉼표 구분자 문자열 계산 테스트")
+    void addWithComma() {
+        final var input = "1,2,3";
+        final var actual = stringCalc.add(input);
+        
+        assertThat(actual).isEqualTo(6);
+    }
+
+    @Test
+    @DisplayName("콜론 구분자 문자열 계산 테스트")
+    void addWithColon() {
+        final var input = "1:2:3";
+        final var actual = stringCalc.add(input);
+        
+        assertThat(actual).isEqualTo(6);
+    }
+
+    @Test
+    @DisplayName("쉼표와 콜론 혼합 구분자 테스트")
+    void addWithMixedDelimiters() {
+        final var input = "1,2:3";
+        final var actual = stringCalc.add(input);
+        
+        assertThat(actual).isEqualTo(6);
+    }
+
+    @Test
+    @DisplayName("빈 문자열 테스트")
+    void addEmptyString() {
+        final var input = "";
+        final var actual = stringCalc.add(input);
+        
+        assertThat(actual).isEqualTo(0);
+    }
+
+    @Test
+    @DisplayName("null 입력 테스트")
+    void addNullInput() {
+        final String input = null;
+        final var actual = stringCalc.add(input);
+        
+        assertThat(actual).isEqualTo(0);
+    }
+
+    @Test
+    @DisplayName("커스텀 구분자 테스트")
+    void addWithCustomDelimiter() {
+        final var input = "//;\n1;2;3";
+        final var actual = stringCalc.add(input);
+        
+        assertThat(actual).isEqualTo(6);
+    }
+
+    @Test
+    @DisplayName("음수 입력 예외 테스트")
+    void addNegativeNumberThrowsException() {
+        final var input = "1,-2,3";
+        
+        assertThatThrownBy(() -> stringCalc.add(input))
+            .isInstanceOf(RuntimeException.class)
+            .hasMessage("음수는 입력할 수 없습니다.");
+    }
+
+    @Test
+    @DisplayName("숫자가 아닌 값 입력 예외 테스트")
+    void addNonNumericValueThrowsException() {
+        final var input = "1,a,3";
+        
+        assertThatThrownBy(() -> stringCalc.add(input))
+            .isInstanceOf(RuntimeException.class)
+            .hasMessage("숫자 이외의 값이 포함되어 있습니다.");
+    }
+
+    @Test
+    @DisplayName("커스텀 구분자와 기본 구분자 혼합 테스트")
+    void addWithCustomAndDefaultDelimiters() {
+        final var input = "//@\n1@2,3:4";
+        final var actual = stringCalc.add(input);
+        
+        assertThat(actual).isEqualTo(10);
+    }
+}
\ No newline at end of file