A battery assy is mounted in a luggage room or beneath the rear seat. In the battery assy, a battery pack having a configuration of an approximate rectangle, when viewed from the side of the vehicle, is stored in an inclined manner in a casing formed of a battery cover and a lower case, having a configuration of an approximate parallelogram, when viewed from the side of the vehicle. A resin chamber is provided at a gap in the frontward position and the rearward position of the battery assy. A channel of cooling air is formed at a gap in the upper region and the lower region of the battery assy. The battery assy is mounted such that the bottom is protruding towards the front of the vehicle.