POWER SUPPLY DEVICE

The power supply device includes a power generator, a drive source, 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 between target amounts of electric power Q, Q, Q, and Q of each battery and measured amounts of electric power M, M, M, and M. The difference summing unit is configured to sum the differences in electric power of the batteries calculated by the difference calculating unit . The electric power summing unit is configured to sum electric power calculated by the difference summing unit and electric power required for the electric motors. A control unit controls the drive source such that electric power calculated by the electric power summing unit is generated by the power generator.