To prevent leakage of a gas even when a float is oscillated in closing a valve in accompany with waving.

A drain trap includes a swing shaft 8 supported in a valve chest 5, a lever 9 and a main arm 10 rotated around the swing shaft 8, a float 12 connected to the lever 9 and floating-up and falling according to a liquid level of the valve chest 5, a lever shaft 11 supported by the lever 9 at a point separating from the swing shaft 8 in parallel with the swing shaft 8, a main arm shaft 14 supported by the main arm 10 at a point separating from the swing shaft 8 and the lever shaft 11 in parallel with the swing shaft 8, a coil spring 16 mounted between the lever shaft 11 and the main arm shaft 14 in a state that both mounting portions are rotatable, a valve arm shaft 17 supported by the main arm 10 at points separating from the swing shaft 8 and the lever shaft 11, and the main arm shaft 14, in parallel with the swing shaft 8, a valve arm 18 rotated around the valve arm shaft 17, and a valve element 20 connected to the valve arm 18 and opening and closing a valve port 6.