A fuel tank includes a tank body having an outer wall formed of a synthetic resin layer having a multilayer structure. The tank body has at least an inner body layer (an inner adhesive layer and an inner base layer) and an outer body layer (a skin layer, an outer base layer, and an outer adhesive layer) between which a barrier layer is interposed. A structure having an air layer therein is attached to the outer side of the skin layer of the outer body layer.