diff --git a/yitou/src/B054_Addition.java b/yitou/src/B054_Addition.java
new file mode 100644
index 0000000000000000000000000000000000000000..2d5d80c51d1d8729ca166eecdc3e60ce30d7ddf4
--- /dev/null
+++ b/yitou/src/B054_Addition.java
@@ -0,0 +1,58 @@
+package src;
+
+import java.util.Scanner;
+
+public class B054_Addition {
+
+  public static void main(final String[] args) {
+    final Scanner scanner = new Scanner(System.in);
+    final String alpha1 = scanner.next().toUpperCase();
+    final String alpha2 = scanner.next().toUpperCase();
+
+    // 足し算メソッドを呼び出す
+    final String result = add(alpha1, alpha2);
+    System.out.println(result);
+
+    scanner.close();
+  }
+
+  // PAIZA表記を足し算する
+  public static String add(final String alpha1, final String alpha2) {
+    // PAIZA表記から10進数へ
+    final int num1 = convertPaizaToDecimal(alpha1);
+    final int num2 = convertPaizaToDecimal(alpha2);
+
+    // 合計
+    final int sum = num1 + num2;
+
+    // 結果をPAIZA表記へ変換
+    return convertDecimalToPaiza(sum);
+  }
+
+  // PAIZA表記から10進数に変換する
+  private static int convertPaizaToDecimal(final String paiza) {
+    int decimalValue = 0;
+
+    for (int i = 0; i < paiza.length(); i++) {
+      final int power = paiza.length() - 1 - i; // 5の階乗
+      decimalValue += PaizaNotation.valueOf(String.valueOf(paiza.charAt(i))).getValue() * Math.pow(5, power);
+    }
+    return decimalValue;
+  }
+
+  //10進数をPAIZA表記に変換する
+  private static String convertDecimalToPaiza(final int decimal) {
+    if (decimal == 0) {
+      return "A"; // 0の場合
+    }
+    final StringBuilder paiza = new StringBuilder();
+    int tempDecimal = decimal; // 引数をコピーする
+
+    while (tempDecimal > 0) {
+      final int remainder = tempDecimal % 5;
+      paiza.insert(0, PaizaNotation.values()[remainder]); // 逆順に挿入
+      tempDecimal /= 5;
+    }
+    return paiza.toString();
+  }
+}
diff --git a/yitou/src/PaizaNotation.java b/yitou/src/PaizaNotation.java
new file mode 100644
index 0000000000000000000000000000000000000000..c6b18c4f5acad95e2d446a464df4497354008788
--- /dev/null
+++ b/yitou/src/PaizaNotation.java
@@ -0,0 +1,22 @@
+package src;
+
+/**
+ * アルファベットを数値に対応させる列挙型です.
+ */
+public enum PaizaNotation {
+  A(0),
+  B(1),
+  C(2),
+  D(3),
+  E(4);
+
+  private final int value;
+
+  PaizaNotation(final int value) {
+    this.value = value;
+  }
+
+  public int getValue() {
+    return value;
+  }
+}
diff --git a/yitou/test/B054_AdditionTest.java b/yitou/test/B054_AdditionTest.java
new file mode 100644
index 0000000000000000000000000000000000000000..5e0da68a3fdb23ca39dc92263863c676249b2164
--- /dev/null
+++ b/yitou/test/B054_AdditionTest.java
@@ -0,0 +1,36 @@
+package test;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import org.junit.jupiter.api.Test;
+import src.B054_Addition;
+
+public class B054_AdditionTest {
+
+  @Test
+  public void AとAを入力したときの出力はAになる() {
+    final String actual = B054_Addition.add("A", "A");
+    final String expected = "A";
+    assertEquals(expected, actual);
+  }
+
+  @Test
+  public void BEBとBCCを入力したときの出力はCCDになる() {
+    final String actual = B054_Addition.add("BAB", "BCC");
+    final String expected = "CCD";
+    assertEquals(expected, actual);
+  }
+
+  @Test
+  public void BBAAとEBBを入力したときの出力はCABBになる() {
+    final String actual = B054_Addition.add("BBAA", "EBB");
+    final String expected = "CABB";
+    assertEquals(expected, actual);
+  }
+
+  @Test
+  public void CとCCCCを入力したときの出力はCCCEになる() {
+    final String actual = B054_Addition.add("C", "CCCC");
+    final String expected = "CCCE";
+    assertEquals(expected, actual);
+  }
+}