An energy storage device is provided with a case including a lid body in which a gas release valve is formed. The gas release valve includes a thin wall with a thickness smaller than a thickness of a portion adjacent to the gas release valve. The thin wall includes an intermediate portion and two lateral portions that are arranged at positions sandwiching the intermediate portion in a first direction. As viewed from a normal direction to the lid body, the intermediate portion is disposed at the middle position in the first direction of the lid body and is formed with a width, in a second direction orthogonal to the first direction, smaller than those of the two lateral portions.