To provide a fuel tank made of a thermoplastic synthetic resin which has a great rigidity, facilitates the production thereof, and enables the reduction of cost.

In the fuel tank 1 made of the thermoplastic synthetic resin which is formed by a blow molding, bead parts 10 which protrude from the outer wall of the fuel tank 1 toward the inside thereof are formed. Each bead part 10 has a plurality of bead convex parts 11 with a large height protruding toward the inside and a plurality of bead concave parts 12 with a small height protruding toward the inside which are alternately successively formed in a lateral direction along the outer wall. The bead convex part 11 has at the inside thereof hollow parts 13 opened to the outer surface of the fuel tank 1 and the bead concave part 12 has connection parts 14 formed by the adhesion of side surfaces at the inside thereof.