A tank cap includes: a synthetic-resin cap body (20) mounted on a fuel supply port cylinder (18) of a conductive fuel tank, (T); a conductive cap shell (22) coupled to an upper part of the cap body (20); and a gasket (23) provided in the cap body (20) and in close contact with a sealing surface (18a) of the fuel supply port cylinder (18). The cap body (20) and the cap shell (22) are linked to be mutually rotatable. A ratchet mechanism (35) is mounted between the cap shell (22) and the cap body (20). An elastic contact piece (38) elastically and slidably contacting an inner peripheral surface of a cylindrical peripheral wall (22a) of the cap shell (22) is integrally projectingly provided on an outer periphery of the gasket (23). Thus, it is possible to cause static electricity carried by an operator to escape to a fuel tank through the gasket.