PURPOSE: To ease assembling work of the fuel tank and the inlet pipe in such a way that a rear cross member which is installed on a floor panel to hold a fuel tank is flexed in the upward and downward directions, and it is formed so as to be able to avoid interference with an inlet pipe.

CONSTITUTION: A tunnel 3 is formed at the center part in the width direction of a floor panel 1, and a fuel tank 4 is held therein. A high part 2A, a middle part 2B, and a low part 2C are provided on a rear cross member 2. An inlet pipe arrangement 10 which is connected at the rear end of the fuel tank 4 is protruded downward at the high part 2A of the rear cross member 2, and it is contrived to be able to be taken out by flexing along the lower side of the middle part 2B in the transverse direction likewise. Thus, the inlet pipe arrangement of the fuel tank can be avoided from interference with the rear cross member without being protruded in the vicinity of a speed change gear, etc. at the rear part of the vehicle, and workability can be improved.