diff --git a/backend/app/__pycache__/main.cpython-312.pyc b/backend/app/__pycache__/main.cpython-312.pyc
index 8c1b95b..bcc55dc 100644
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diff --git a/backend/app/main.py b/backend/app/main.py
index 23ed1f8..0e5af8d 100644
--- a/backend/app/main.py
+++ b/backend/app/main.py
@@ -42,3 +42,6 @@ app.include_router(ledger_router)
 from app.modules.trial_balance.router import router as trial_balance_router
 app.include_router(trial_balance_router)
 
+from app.modules.opening_balances.router import router as opening_router
+app.include_router(opening_router)
+
diff --git a/backend/app/modules/journals/schemas.py b/backend/app/modules/journals/schemas.py
new file mode 100644
index 0000000..f131588
--- /dev/null
+++ b/backend/app/modules/journals/schemas.py
@@ -0,0 +1,29 @@
+# app/modules/journals/schemas.py
+from pydantic import BaseModel, field_validator
+from typing import List
+from decimal import Decimal
+from datetime import date
+
+class JournalLineCreate(BaseModel):
+    account_id: int
+    debit: Decimal = 0
+    credit: Decimal = 0
+
+    @field_validator("debit", "credit")
+    @classmethod
+    def non_negative(cls, v):
+        if v < 0:
+            raise ValueError("金額は0以上で入力してください")
+        return v
+
+class JournalCreate(BaseModel):
+    journal_date: date
+    description: str
+    lines: List[JournalLineCreate]
+
+    @field_validator("lines")
+    @classmethod
+    def validate_lines(cls, v):
+        if len(v) < 2:
+            raise ValueError("仕訳明細は2行以上必要です")
+        return v
diff --git a/backend/app/modules/opening_balances/__init__.py b/backend/app/modules/opening_balances/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/backend/app/modules/opening_balances/__pycache__/__init__.cpython-312.pyc b/backend/app/modules/opening_balances/__pycache__/__init__.cpython-312.pyc
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index 0000000..61681c5
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diff --git a/backend/app/modules/opening_balances/__pycache__/router.cpython-312.pyc b/backend/app/modules/opening_balances/__pycache__/router.cpython-312.pyc
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index 0000000..6a6fd76
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diff --git a/backend/app/modules/opening_balances/__pycache__/schema.cpython-312.pyc b/backend/app/modules/opening_balances/__pycache__/schema.cpython-312.pyc
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index 0000000..14d10b2
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diff --git a/backend/app/modules/opening_balances/router.py b/backend/app/modules/opening_balances/router.py
new file mode 100644
index 0000000..4b40f4a
--- /dev/null
+++ b/backend/app/modules/opening_balances/router.py
@@ -0,0 +1,55 @@
+# backend/app/modules/opening_balances/router.py
+from fastapi import APIRouter, HTTPException
+from psycopg.errors import ForeignKeyViolation
+from app.core.database import get_connection
+from app.modules.opening_balances.schema import OpeningBalanceCreate
+
+router = APIRouter(
+    prefix="/opening-balances",
+    tags=["期首残高"]
+)
+
+@router.post("/", summary="期首残高 登録/更新")
+def upsert_opening_balance(data: OpeningBalanceCreate):
+    try:
+        with get_connection() as conn, conn.cursor() as cur:
+            cur.execute("""
+                INSERT INTO opening_balances
+                    (fiscal_year, account_id, opening_debit, opening_credit)
+                VALUES (%s, %s, %s, %s)
+                ON CONFLICT (fiscal_year, account_id)
+                DO UPDATE SET
+                    opening_debit = EXCLUDED.opening_debit,
+                    opening_credit = EXCLUDED.opening_credit
+            """, (
+                data.fiscal_year,
+                data.account_id,
+                data.opening_debit,
+                data.opening_credit
+            ))
+            conn.commit()
+        return {"result": "ok"}
+
+    except ForeignKeyViolation:
+        raise HTTPException(
+            status_code=400,
+            detail="存在しない科目が指定されています"
+        )
+
+
+@router.get("/{fiscal_year}", summary="期首残高一覧取得")
+def list_opening_balances(fiscal_year: int):
+    with get_connection() as conn, conn.cursor() as cur:
+        cur.execute("""
+            SELECT
+                a.account_code,
+                a.account_name,
+                a.account_type,
+                ob.opening_debit,
+                ob.opening_credit
+            FROM opening_balances ob
+            JOIN accounts a ON a.account_id = ob.account_id
+            WHERE ob.fiscal_year = %s
+            ORDER BY a.account_code
+        """, (fiscal_year,))
+        return cur.fetchall()
diff --git a/backend/app/modules/opening_balances/schema.py b/backend/app/modules/opening_balances/schema.py
new file mode 100644
index 0000000..0133545
--- /dev/null
+++ b/backend/app/modules/opening_balances/schema.py
@@ -0,0 +1,25 @@
+# backend/app/modules/opening_balances/schema.py
+from pydantic import BaseModel, field_validator
+
+class OpeningBalanceCreate(BaseModel):
+    fiscal_year: int
+    account_id: int
+    opening_debit: float = 0
+    opening_credit: float = 0
+
+    @field_validator("fiscal_year")
+    @classmethod
+    def validate_year(cls, v: int):
+        if v < 2000 or v > 2100:
+            raise ValueError("会计年度不正确")
+        return v
+
+    @field_validator("opening_credit")
+    @classmethod
+    def validate_balance(cls, v, info):
+        debit = info.data.get("opening_debit", 0)
+        if debit > 0 and v > 0:
+            raise ValueError("借方和贷方不能同时输入金额")
+        if debit < 0 or v < 0:
+            raise ValueError("金额不能为负数")
+        return v