To provide an exhaust valve having a large vacuum breakage capacity, which can quickly perform vacuum breakage.

There is formed a valve chamber 3 which is a casing composed of a body 1 and a lid 2, and whose flow-in port 4 is opened at a lower part and whose flow-out port 5 is opened at an upper part. A valve seat 6 is formed between the valve chamber 3 and the flow-out port 5. The body 1 integrally has a plurality of inwardly-protruding ribs 9 at the inner wall of the valve chamber 3, and fixes a substantially-cylindrical bottomed float receiver 10 having a penetration hole 11 small in opening area at the bottom to the inside of the ribs 9. A spherical float 12 is arranged in the float receiver 10 in a free state. A substantially-disc shaped barrier diversion member 13 is fixed to the flow-out port 5. The barrier diversion member 13 has, in its center, a barrier 14 and a diversion part having a large number of small gaps 15 opened around itself. Each small gap 15 is opened obliquely downward toward the inner wall of the valve chamber 3. Outside air is hindered to linearly progress toward the center of the valve chamber 3 by the barrier wall diversion member 13, reduced in speed, and diffused into the valve chamber 3 toward the inner wall of the valve chamber 3 from the small gap 15 at a moderate speed.