A battery unit comprises plural side connection portions which are provided at its both-side end portions in a vehicle width direction and connected to said vehicle-body member, and these connection portions are connected to a high rigidity portion of a vehicle-body member, concretely, to the vehicle-body member at a specified position where floor cross members integrally connected to a vehicle floor panel are located, to the vehicle-body member at a specified position where a torque box is located, or to the vehicle-body member at a specified position where a kick-up portion of the vehicle floor panel is located. Accordingly, the torsional rigidity of the vehicle body can be increased by utilizing the battery unit mounted below the vehicle body floor (vehicle floor panel).