There are provided a floor panel, a pair of right-and-left floor frames, and a battery unit supporting a battery module and mounted at the floor frames. The battery unit comprises the battery module, a pair of right-and-left side frames mounted at the pair of floor frames, and a pair of front-and-rear module supporting mechanisms which comprises a pair of front-and-rear cross frames respectively extending in a vehicle width direction and interconnecting the pair of side frames and mounting brackets supporting a front end portion and a rear end portion of the battery module. Bending rigidity, in a vertical direction, of the module supporting mechanism comprising the third cross frame and the first mounting bracket is set to be lower than that of the side frame.