A threaded fastener includes a bolt and a washer. The washer has a washer main body and a seal member provided at an outer peripheral side of the washer main body. The washer is caulked and fixed to a shank portion of the bolt in a water stop state, and the seal member is in contact with a fastened member in a water stop state, with a bearing surface of the washer main body held in contact with the fastened member. The seal member is provided on its outer periphery with a protrusion portion that protrudes outward beyond a radially outer end of a contact portion of the seal member with the washer in a no-load state. A back surface of the protrusion portion on the opposite side of the fastened member is an inclined surface.