A power supply device for a vehicle includes: a first energy storage device having a first energy storage element; a second energy storage device having a second energy storage element; a switch which switches between a state in which the first energy storage device and the second energy storage device are connected in parallel and a state in which the first energy storage device and the second energy storage device are separated from each other; and a switch controller. Each of the first energy storage element and the second energy storage element is an energy storage element having an SOC-OCV characteristic having a flat region thereon, and the switch controller switches the switch from an off-state to an on-state when each of the first energy storage element and the second energy storage element is in the flat region of the SOC-OCV characteristic.