In a power supply unit disposed below a floor behind a seat, battery modules are disposed in a lower position, and a DC/DC converter and a motor driving inverter are disposed side by side in a vehicle width direction above the battery modules. Thus, cooling air flowing from the front side to the rear side of a vehicle body is divided into upper and lower portions to cool in parallel the DC/DC converter and the motor driving inverter on the upper side and the battery modules on the lower side. Thus, it is possible to simplify a passage of the cooling air to reduce the size of the entire power supply unit, and improve mountability of the power supply unit on the vehicle body. Also, it is possible to apply low temperature cooling air, before heat exchange, to the battery module, the DC/DC converter, and the motor driving inverter.