A fuel tank is provided which suppresses wave motion on the liquid surface of fuel which occurs when a vehicle accelerates or decelerates. A front wall and/or a rear wall of the fuel tank includes a plurality of steps formed integrally therewith. The liquid surface of the fuel striking the steps is dispersed, and wave motion on the liquid surface is thereby suppressed. Since the steps are formed in the front wall and/or the rear wall of the fuel tank, the volume of the tank is not reduced.