To prevent water from leaking even when water sharply flows from an inlet into a valve chest.

The valve chest 3 is formed of a casing comprising a body 1 and a lid 2 and having the inlet 4 opened on a lower part and an outlet 5 opened on an upper part. A valve seat 6 is formed between the valve chest 3 and the outlet 5. The body 1 integrally has a plurality of ribs 9 projecting inward on the inner wall of the valve chest 3, and a bottomed float receiver 10, which is formed in almost cylindrical shape and has a through hole 13 with a large opening area for communication with the inside and the outside, is arranged inside the rib 9. A spherical float 12 is arranged in a free state in the float receiver 10. A water flow receiving member 14 is provided to change the opening area of the through hole 13. The water flow receiving member 14 increases the opening area of the through hole 13 by the force of water sharply flowing from the inlet 4 into the valve chest 3.