PURPOSE: To suppress as much as possible the deformation toward the direction of vehicular chamber of the kick-up portion of the rear floor by contacting the rear bottom of a reinforcement with the bottom of the rear side frame.

CONSTITUTION: The front end of a reinforcement 9 is positioned on the rear side of the vehicular body rather than a bent slope portion 4d, and the rear is positioned close to the rear of a frame member 4. The front of the reinforcement 9 of a U-shaped cross section is of atriple structure to be joined with a side-still inner 6 through the frame member 4. The vertical wall 9b is welded to the inside vertical wall 4b of the vehicular body at every a given interval from the front end to the rear end, and the rear is of a triple structure to be joined with a tire house inner through the frame member 4, having a wide width than the front.