To provide an exhaust valve having an extensive vacuum break ability and capable of effecting quick vacuum break.

A casing having a body 1 and a lid 2 forms a valve chest 3 having an inflow port 4 opening at its lower part and an outflow port 5 opening at its upper part, and a valve seat 6 is formed between the valve chest 3 and the outflow port 5. The body 1 integrally has, at the inner wall of the valve chest 3, a plurality of ribs 9 protruding inward, and a virtually cylindrical, bottomed float receiver 10 having at its bottom a through-hole 11 with a small opening area is fixed at the inner side of the ribs 9 by a snap ring. A spherical float 12 is placed in the float receiver 10 in a free state, and the lid 2 integrally has a deflection member 13 at the inner wall of the outflow port 5 via a plurality of ribs 14. The deflection member 13 is conical and is positioned substantially in the center of the outflow port 5 to guide outside air to the inner wall of the valve chest 3. The outside air guided by the deflection member 13 to the inner wall of the valve chest 3 hardly flows into the float receiver 10, so that it rarely bounces off the bottom of the float receiver 10, and pressure hardly rises at the lower part of the float 12 within the float receiver 10. Accordingly, the float 12 hardly floats up.