PURPOSE: To stabilize mounting of a foot rest, to reduce the size and the weight of the foot rest, and to improve appearance of the foot rest.

CONSTITUTION: The width of the rear part 5b of a floor tunnel 5 spaced away from a dash board 1 is narrower than that of the front part 5a of the floor tunnel located near the dash board. A intermediate part between the front part and the rear part of the floor tunnel is short. At the intermediate part, the width of the floor tunnel is rapidly changed, and mounting holes for mounting a foot rest 7 are formed in a vertically arranged state in the side panels 6b and 6c of the intermediate part. The foot rest wherein the mounting holes are formed on the working line of a force generated when a foot is placed on the foot rest is fixed by means of opening holes and the mounting holes.