To provide an exhaust valve high in vacuum break capacity to quickly carry out vacuum break.

A valve chamber 3 is formed of a main body 1 and a lid 2, and has an inflow port 4 opening at a lower portion thereof and an outlet port 5 opening at an upper portion thereof. The main body 1 has a plurality of ribs 9 projecting inwardly from an inner wall of the valve chamber 3 and integrally disposed thereto, a bottomed and substantially cylindrical float receiver 10 is fixed to the inside of ribs 9 and has a through hole 11 small in opening area at a bottom portion thereof, and a spherical float 12 is disposed in a free state in the float receiver 10. An approximately disc-shaped blocking and separating member 13 is fixed to the outlet port 5. The blocking and separating member 13 has a blocking portion 14 at the center thereof, and a separating portion in which many small clearances are formed at the circumference thereof. Outside air is blocked by the blocking portion 14 and decelerated by the separating member 13 to be diffused in the valve chamber 3 in lower speed. Accordingly, the outside air is not susceptible to flowing onto and returning from the bottom portion of the float receiver 10, so that the float 12 is difficult to float up and high vacuum break capacity is implemented to quickly carrying out vacuum break.