To smoothly move up and down a valve element in the vertical direction by devising a guide method for the valve element.

A floater 26 adapted to move up and down by water pressure includes: a rod 26b slidably guided by a guide hole 25c of a V-case 25; and a projection-like rib 26d slidably abutted on the inner wall of the V-case 25. In this example, the rod 26 is abutted at one portion to the guide hole 25c, and the rib 26d is abutted at one portion to the inner wall surface of the V-case 25, whereby the attitude of the floater 26 is maintained at two portions.