A power supply apparatus includes a plurality of battery modules, a support plate, a plurality of first reinforcing projections, and a plurality of second reinforcing projections. The support plate supports the battery modules and includes a first plate and a second plate. The first plate thermally contacts bottom surfaces of the battery modules. The second plate is placed on a bottom surface of the first plate to define cooling spaces between the first and second plates. A coolant is to flow in the cooling spaces. The plurality of first reinforcing projections is provided on at least one of the first and second plates. The first reinforcing projections project into the cooling spaces and extend in a first direction. The plurality of second reinforcing projections is provided on a top surface of the first plate and extending in a second direction intersecting with the first direction.