To provide an exhaust valve closing after completing the exhaust even when a pressure in a inlet side is high.

A valve chest 3 having an inlet 4 and an outlet 5 opened in its lower part and in its upper part respectively is formed of a casing comprising a body 1 and a lid 2. A valve seat 6 is formed between the valve chest 3 and the outlet 5. The body 1 is integrally provided with a plurality of ribs 9 projecting to the inside in the inner wall of the valve chest 3 and a cylindrical bottomed float receiver 10 having a through hole 11 in its bottom is fixed to the inside of the rib 9. A spherical float 12 is disposed in the float receiver 10 in the free state. A lowering position adjusting member 13 adjusting the lowering position of the float 12 is screwed to the bottom part of the float receiver 10 and loosely fixed thereto by a lock nut 14. The lowering position adjusting member 13 is integrally provided with a barrier member 15 obstructing the straight passing of the fluid from the inlet 4 to the through hole 11 in its upper part.