According to the invention, a fuel tank for storing a fuel therein is provided. The fuel tank comprises a pair of spaced deformable thin walls (5,6) and a deformable connecting wall (7) extending between peripheral edges of the thin walls. The connecting wall and the thin walls define a fuel chamber (3) therein. The thin walls and the connecting wall are connected with each other to cause the connecting wall to expand inwardly when the thin walls expand outwardly.