A power storage device including a battery containing body and a first guide rail for receiving a first end portion on a lower side of the body and a second guide rail for receiving a second end portion on an upper side of the body. The first guide rail includes a higher side plate and a lower side plate and extend in an insertion direction, and a receiving portion including a stopper. A first protrusion portion that, when removing the battery containing body, engages with the stopper, thereby preventing the battery containing body from dropping A second protrusion portion that, when the battery containing body is turned upside down, engages with the higher side plate, thereby blocking the insertion. When an attempt to remove the battery containing body from the receiving portion is made, the second protrusion portion engages with the stopper, thereby preventing it from dropping.