diff --git a/knoda/src/B087_HiddenNumber.java b/knoda/src/B087_HiddenNumber.java
new file mode 100644
index 0000000000000000000000000000000000000000..31180c931bfe0a91841bfc9837ea3f983400f8be
--- /dev/null
+++ b/knoda/src/B087_HiddenNumber.java
@@ -0,0 +1,85 @@
+package hellojunit;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Scanner;
+
+public class B087_HiddenNumber {
+
+	public static void main(String[] args) {
+		final Scanner scan = new Scanner(System.in);
+		final int height = scan.nextInt();
+		final int width = scan.nextInt();
+		final int digits = scan.nextInt();
+		// マスに数字を入力する
+		final List<String> board = new ArrayList<String>();
+		for (int i = 0; i < height; i++) {
+			board.add(scan.next());
+		}
+		HiddenNumber hiddenNumber = new HiddenNumber();
+		// 最大の数を取得する
+		final int max = hiddenNumber.getMaxNumber(board, digits);
+		System.out.println(max);
+		scan.close();
+	}
+
+}
+
+class HiddenNumber {
+	private final int MIN_NUMBER = 1; // 値を比較するときに用いる初期値
+	
+	// 最大の数を取得するメソッド
+	public int getMaxNumber(final List<String> board, final int digits) {
+		int max = MIN_NUMBER;
+		max = getMaxNumber(board, digits, max);
+		// switchRowAndColumnBoard : マスの縦と横を入れ替えたときの状態
+		final List<String> switchRowAndColumnBoard = getSwitchRowAndColumn(board);
+		max = getMaxNumber(switchRowAndColumnBoard, digits, max);
+		return max;
+	}
+	
+	// それぞれの基盤(マスの縦と横を入れ替えた2つの基盤)の最大の数を取得するメソッド
+	private int getMaxNumber(final List<String> board, final int digits, int max) {
+		for (final String row : board) {
+			for (int i = 0; i < row.length() - digits + 1; i++) {
+				final int number = exchangeStringForInteger(row, i, digits);
+				if (max < number) {
+					max = number;
+				}
+			}
+		}
+		return max;
+	}
+	
+	// マスの縦と横を入れ替えるメソッド
+	private List<String> getSwitchRowAndColumn(final List<String> board) {
+		final List<String> switchRowAndColumn = new ArrayList<String>();
+		for (int i = 0; i < board.get(0).length(); i++) {
+			final List<Character> charList = new ArrayList<Character>();
+			for (int j = 0; j < board.size(); j++) {
+				charList.add(board.get(j).charAt(i));
+			}
+			switchRowAndColumn.add(exchangeCharForString(charList));
+		}
+		return switchRowAndColumn;
+	}
+	
+	// 文字列を整数値に変換するメソッド
+	private int exchangeStringForInteger(final String row, final int startIndex, final int digits) {
+		final List<Character> charList = new ArrayList<Character>();
+		for (int i = startIndex; i < startIndex + digits; i++) {
+			charList.add(row.charAt(i));
+		}
+		return Integer.parseInt(exchangeCharForString(charList));
+	}
+	
+	// 文字を文字列に変換するメソッド
+	private String exchangeCharForString(final List<Character> charList) {
+		StringBuilder sb = new StringBuilder();
+		for (Character ch : charList) {
+			sb.append(ch);
+		}
+		return sb.toString();
+	}
+	
+}
diff --git a/knoda/test/B087_HiddenNumberTest.java b/knoda/test/B087_HiddenNumberTest.java
new file mode 100644
index 0000000000000000000000000000000000000000..359d3773412d0b123ae5ec63268826350892a8e3
--- /dev/null
+++ b/knoda/test/B087_HiddenNumberTest.java
@@ -0,0 +1,61 @@
+package hellojunit;
+
+import static org.hamcrest.CoreMatchers.*;
+import static org.junit.Assert.*;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+
+import org.junit.Test;
+
+public class B087_HiddenNumberTest {
+
+	@Test
+	public void テスト1() {
+		final List<String> board = new ArrayList<String>(Arrays.asList(
+				"66737",
+				"56173",
+				"59414",
+				"25469",
+				"63955"
+				));
+		final int digits = 3;
+		HiddenNumber hiddenNumber = new HiddenNumber();
+		final int expected = 955;
+		final int actual = hiddenNumber.getMaxNumber(board, digits);
+		assertThat(actual, is(expected));
+	}
+	
+	@Test
+	public void 出力が87になるテスト() {
+		final List<String> board = new ArrayList<String>(Arrays.asList(
+				"77777",
+				"77777",
+				"77777",
+				"77778",
+				"77787"
+				));
+		final int digits = 2;
+		HiddenNumber hiddenNumber = new HiddenNumber();
+		final int expected = 87;
+		final int actual = hiddenNumber.getMaxNumber(board, digits);
+		assertThat(actual, is(expected));
+	}
+	
+	@Test
+	public void 出力が9876になるテスト() {
+		final List<String> board = new ArrayList<String>(Arrays.asList(
+				"12345",
+				"54321",
+				"67891",
+				"19876"
+				));
+		final int digits = 4;
+		HiddenNumber hiddenNumber = new HiddenNumber();
+		final int expected = 9876;
+		final int actual = hiddenNumber.getMaxNumber(board, digits);
+		assertThat(actual, is(expected));
+	}
+
+}