POWER SUPPLY DEVICE

A power supply device includes a power generator, a drive source, a plurality of power supply lines, a plurality of batteries, a difference calculating unit , a difference summing unit , and an electric power summing unit . The difference calculating unit is configured to calculate differences D, D, D, and D between a target charge state set for each battery and an estimated charge state. The difference summing unit is configured to sum the differences D, D, D, and D calculated by the difference calculating unit . The electric power summing unit is configured to sum the charge state calculated by the difference summing unit and electric power used for the electric loads. A control unit controls the drive source such that electric power calculated by the electric power summing unit is generated by the power generator.