In a rack-mount power supply device, a plurality of battery packs are removably placed in a rack main body. In each battery pack, a battery including a plurality of unit cells is housed in an outer case, and positive and negative output terminals are provided so as to come out on a back surface of the outer case. The rack main body includes a plurality of housing spaces housing the battery packs, respectively, and includes input terminals on a facing surface which is an inner surface of each housing space and which faces output terminals, the output terminals being to be electrically connected to the input terminals in a fitting state. In the rack main body, the input terminals are wired in a predetermined connection state on the back sides of the respective facing surfaces. In the rack-mount power supply device, the plurality of battery packs are connected to each other in a predetermined connection state, with the plurality of battery packs guided into the housing spaces of the rack main body and the output terminals connected to the input terminals.