To make drain in a drain inflow pipe easily flow down to a valve chest through an inlet.

An inlet 3, a valve chest 7 having the inlet 3 at its upper portion, a valve port 8 formed at a lower portion of the valve chest 7, and an outlet 5 communicated from the valve chest 7 through the valve port 8, are formed on a casing composed of a body 1 and a cover body 6. A float 12 floating up or falling according to a liquid level of the valve chest 7 to open and close the valve port 8 through a lever 11 and a valve element 16, is disposed in the valve chest 7. An inflow port 2 formed on an upper portion of the inlet 3 and connected to a drain inflow pipe, is formed on the casing, and an upper part of the inlet 3 of the valve chest and the inflow port 2 are communicated by a balance passage 4. As water head difference C can be secured between the center A of the inflow port 2 connected to the drain inflow pipe and the center B of the inlet 3, the drain in the drain inflow pipe can easily flow down to the valve chest 7 through the inlet 3 from the inflow port 2.