According to one embodiment, a storage device includes an enclosure, and a circuit board assembly in the enclosure. The circuit board assembly includes a first circuit board on which a heat-producing component is mounted, a second circuit board, a third circuit board, a first connector connecting the first and second circuit boards, a second connector connecting the second and third circuit boards, a first spacer sandwiched between the first and second circuit boards, and a second spacer sandwiched between the second and third circuit boards. The first spacer includes a spacer frame, a partition member opposed to the heat-producing component with a gap between, and a thermal transfer member attached to the partition member and in contact with the first circuit board.