A power supply device includes a first power supply circuit, a second power supply circuit, and a power supply-switching unit. The first power supply circuit includes a power storage device having a first capacity and supplies electricity of a first voltage to the electric motor. The second power supply circuit includes a power storage device having a second capacity smaller than the first capacity and supplies electricity of a second voltage higher than the first voltage to the electric motor. The power supply-switching unit supplies electricity from the second power supply circuit to the electric motor at the tune of starting an operation of the electric motor and thereafter supplies electricity from the first power supply circuit to the electric motor.