Provided is a power supply apparatus that can be disposed below a floor panel of a vehicle, including: a wiring structural body that is disposed below the floor panel, and is routed such that a first high-voltage wire harness, a second high-voltage wire harness, and a low-voltage wire harness extend along the wiring structural body; a high-voltage electricity storage device disposed below the wiring structural body; a first low-voltage electricity storage device and a second low-voltage electricity storage device that are disposed below the wiring structural body; and a 100-V charger, a first DC/DC converter, and a second DC/DC converter that are disposed below the wiring structural body.