A vehicle power source device includes a power source backup unit using a capacitor unit formed by a plurality of capacitors as an auxiliary power source. The vehicle power source device has a power supply section for enabling power supply from the power source capacitor unit to an electronic control section and a forced operation section for operating the power supply section. Even during normaloperation of a battery, the operation state of its power supply section is checked, thereby providing a vehicle power source device having a high reliability and safety.