A lead wire is electrically connected to an electric power source. A wire heater is supplied with electric power through the lead wire to generate heat. An insertion hole is formed in a housing. The lead wire and the wire heater are connected by a caulked member and fixed to each other, while aligning the tips of the lead wire and the wire heater in the same direction. The lead wire and the wire heater, connected by the caulked member, are fixed in the insertion hole with being inserted from the inlet portion of the insertion hole toward the end portion of the insertion hole. Sealing resin is injected into the insertion hole from an injection hole formed in the end portion, and filled therein.