A battery pack locked to a vehicle body for mounting to and detaching from the vehicle body. A battery case is provided with an extension part extending to above a battery cell accommodating part. The extension part includes a handle including a grip part having an orientation set so as to extend in the vehicle longitudinal direction when the battery case is mounted on the vehicle. The handle is provided on the battery case in the state of being deviated toward either of vehicle-width-directionally left and right sides. A lock device attached to a main frame of the electric vehicle is provided with a lock pin that is advanced and retracted. The extension part on the battery case side is provided with an engagement hole for accepting the lock pin, the engagement hole being formed in either of side surface portions in the longitudinal direction of the electric vehicle.