A rack-mount power supply device comprising: a plurality of battery packs; and a rack main body allowing the battery packs to be removably placed therein, wherein each of the battery packs comprises: a battery including a plurality of unit cells connected in series and/or parallel with each other; an outer case housing the battery; and positive and negative output terminals provided so as to come out on a back surface of the outer case, and connected to an output side of the battery, wherein the rack main body includes a plurality of housing spaces housing the battery packs in fixed positions, respectively, and includes input terminals on a facing surface being an inner surface of each of the housing spaces and facing positive and negative output terminals provided to a corresponding battery pack, the output terminals being to be electrically connected to the input terminals in a fitting state, and the input terminals are wired in series and/or parallel with each other on back sides of the respective facing surfaces, and the plurality of battery packs are connected in series and/or parallel with each other, with the battery packs guided into the housing spaces of the rack main body and the output terminals connected to the input terminals, characterized in that each of the battery packs further comprises: an electronic circuit detecting and monitoring states of the plurality of unit cells; a shutdown circuit controlling the electronic circuit to ON or OFF; and placement detection terminals detecting that the battery pack has been placed in the fixed position of the rack main body, the rack main body includes coupling terminals to be connected to the placement detection terminals with the battery pack placed in the fixed position, and the shutdown circuit places the electronic circuit in an ON state when the placement detection terminals and the coupling terminals are in a connected state, and places the electronic circuit in an OFF state when the placement detection terminals and the coupling terminals are in a non-connected state. a plurality of battery packs; and a rack main body allowing the battery packs to be removably placed therein, wherein each of the battery packs comprises: a battery including a plurality of unit cells connected in series and/or parallel with each other; an outer case housing the battery; and positive and negative output terminals provided so as to come out on a back surface of the outer case, and connected to an output side of the battery, wherein a battery including a plurality of unit cells connected in series and/or parallel with each other; an outer case housing the battery; and positive and negative output terminals provided so as to come out on a back surface of the outer case, and connected to an output side of the battery, the rack main body includes a plurality of housing spaces housing the battery packs in fixed positions, respectively, and includes input terminals on a facing surface being an inner surface of each of the housing spaces and facing positive and negative output terminals provided to a corresponding battery pack, the output terminals being to be electrically connected to the input terminals in a fitting state, and the input terminals are wired in series and/or parallel with each other on back sides of the respective facing surfaces, and the plurality of battery packs are connected in series and/or parallel with each other, with the battery packs guided into the housing spaces of the rack main body and the output terminals connected to the input terminals, an electronic circuit detecting and monitoring states of the plurality of unit cells; a shutdown circuit controlling the electronic circuit to ON or OFF; and placement detection terminals detecting that the battery pack has been placed in the fixed position of the rack main body, the rack main body includes coupling terminals to be connected to the placement detection terminals with the battery pack placed in the fixed position, and the shutdown circuit places the electronic circuit in an ON state when the placement detection terminals and the coupling terminals are in a connected state, and places the electronic circuit in an OFF state when the placement detection terminals and the coupling terminals are in a non-connected state.