A vehicle power supply device includes: a plug socket to supply an external device with electrical power; and an external output switch configured to be switched between an on state in which the electrical power is supplied from a battery to the plug socket and an off state in which the supply of the electrical power is stopped. In a case where the external output switch is in the on state, when the vehicle transitions from a ready mode to an OFF mode, the switch control unit sets the external output switch to the off state along with the transition, and when the vehicle transitions from an ACC mode or an ON mode to the OFF mode, the switch control unit maintains the on state of the external output switch.