PURPOSE: To withstand impact without increasing the strength of the side wall of a fuel tank so as to make the fuel tank lightweight by providing an impact damper for absorbing the inertia of fuel to relax impact, on the tank side wall inner surface upon which impact load acts.

CONSTITUTION: An impact damper formed of an air bag 6 is fitted to the front face of a fuel cell 4, in contact with the inside of the front wall 2 of a metal tank 1. As a result, in the case of impact load at the time of forced landing or the like acting frontward upon the fuel tank, the inertial force of fuel is caught by the impact damper formed of the air bag 6 so as to lighten the impact load acting upon the front wall 2 of the metal tank 1. In the case of being shot by a missile or the like, the pressure of fuel is instantaneously heightened since the missile advances rapidly in the fuel cell 4, but the impact force is relaxed, and the damaged area is reduced.