A hybrid drive system includes first and second power supply devices that supply direct-current power; first and second power storage devices are respectively connected to the first and second power supply devices so as to accumulate or discharge the direct-current power; a first load device that receives a supply of the direct-current power from the first power supply device and the first power storage device and drives a first load; and a second load device that receives a supply of the direct-current power from the second power supply device and the second power storage device and drives a second load. The hybrid drive system includes an inter-group contactor for electrically connecting and disconnecting input terminals of the first power storage device and the second power storage device.