Resin component welding structure

A fuel tank (11) has a body (1) formed of resin having low permeability to hydrocarbon gases. A resin (10) is insert molded to the connecting portion of body that connects with a connecting portion of tank and which is weldable to fuel tank. A packing material (7) has low permeability to hydrocarbon gases is fixed to body such that the packing material is interposed between body and insert molded resin. The fuel tank has resin inner and outer shells (12,13) interposed by a fuel permeation prevention layer such that they are laminated. A resin component is attached to the fuel tank.