To solve the problem of a conventional vacuum breaker that water is leaked from an air intake port to dirty the floor surface inside a toilet space because seal of the air intake port is imperfect caused by the scale, silica or calcium carbonate adhering to a sheet packing or the periphery thereof of a flush toilet stool with a longtime use, depending on the quality of water.

This vacuum breaker formed of a valve seat body having the air intake port, an upper casing and a lower casing has an air intake port formed of a clearance between the upper casing and the lower casing. A water receiver part for storing the water leaked from the sheet packing is formed in the periphery of the vacuum breaker. Even if the scale adheres to the sheet packing and the periphery thereof and the air intake port can not be perfectly sealed, the leaked water is stored in the water receiver part to protect the floor surface of the toilet space from dirt.