A power supply device includes battery circuit modules each having a battery, a first switching element S1 connected in parallel to the battery, and a second switching element S2 connected in series to the battery between the battery and the first switching element S1, the second switching element S2 being turned off when the first switching element S1 is turned on, a battery circuit module group in which the battery circuit modules are connected in series, and a control circuit for outputting, at intervals of a certain time, a gate signal for turning on and off the first switching element S1 and the second switching element S2 to the battery circuit modules.