POWER SUPPLY DEVICE

PROBLEM TO BE SOLVED: To provide a power supply device capable of suppressing a shortage of capacity in a power supply supplying a current to a control device of each battery pack depending on a state of a switch, in a power supply device mounting a plurality of battery packs.SOLUTION: A power supply device 10 comprises: battery packs 20-1, 20-2, and 20-3 each having a battery stack 21, a relay 22, and a control device 23 controlling the relay 22; and a switch 12 having an on state in which supply of power to an external load 11 is permitted, and an off state in which the supply of power is forbidden. Each control device 23 comprises: a constant current generation part 24; and a current measurement part 25, and outputs a constant current from the constant current generation part 24 and controls the relay 22 to the on state depending on a current measurement value of the current measurement part 25. Each constant current generation part 24 outputs a DC current to the current measurement part 25 different from each other. The switch 12 is inserted into a circuit connecting between the constant current generation part 24 and the current measurement part 25.