Provided is a power storage device including: a first chassis member; a second chassis member; a power inlet; one or plural power outlets; a battery module; a power conversion device; a housing; a lower lid; and an upper lid. The battery module is fixed closely to one surface of the first main surface portion. The power conversion device is fixed closely to one surface of the second main surface portion. A gap portion is formed between the first main surface portion and the second main surface portion by disposing the other surface of the first main surface portion and the other surface of the second main surface portion to face each other. The space is used to make air taken through the plural openings of the lower lid flow via the plural openings of the upper lid.