To improve sealing between an outlet pipe and an inlet pipe by sufficiently securing the seal surface distance of seal members between the outlet pipe and the inlet pipe.

A holding member 5 is provided on one end 12a side of an inlet pipe 12 of a valve mechanism part, the outside diameter of a collar part 52 of the holding member 5 is approximately equal to the outside diameter D4 of an outlet pipe 11 of a water temperature adjusting part, and the outside diameter of a packing 7 to be arranged between the collar part 52 and one end 11a of the outlet pipe 11 is approximately equal to the outside diameter D4. Therefore, the area for holding the packing 7 can be increased in comparison with a pipe connecting structure in which the collar part 52 is not provided, moreover, the seal surface distance of the packing 7 can be increased.