A battery box housing a battery is mounted between left and right side frames extending in a longitudinal direction of a vehicle body so that the battery box is offset to a left side of the vehicle body, and an intake duct and an exhaust duct for cooling air for cooling the battery are connected to an end of the battery box on a right side of the vehicle body. Therefore, it is possible not only to protect the battery between the left and right frames from a shock caused upon a side collision, but also to ensure a space for disposition of the intake duct and the exhaust duct while ensuring a volume of the battery box to the maximum. Moreover, the battery box is connected at its left and right ends to the left and right side frames.