A semiconductor storage device includes a substrate having a wiring, a first semiconductor memory, a terminal portion, a holder surrounding the terminal portion, a case, and a first plate-shaped member. The first semiconductor memory is disposed on a first principal surface of the substrate and is connected to the wiring. The terminal portion is connected to the substrate at a first end portion of the substrate and has a terminal connected to the wiring. The case houses part of the holder, the substrate, and the first semiconductor memory. Between the first principal surface and a first wall portion of the case facing the first principal surface, the first plate-shaped member is disposed. The first plate-shaped member is connected to the holder and the first principal surface on a second end portion side of the substrate, and has thermal conductivity.