To prevent leakage of gas even when a float is swung together with bubbling at the time of a valve being closed.

The float type drain trap comprises: a swing shaft 8 supported in a valve chamber 5; a lever 9 and a main arm 10 rotating around the swing shaft 8; a float 12 coupled with the lever 9 and moving upward and downward according to a liquid level of the valve chamber 5; a lever shaft 11 supported by the lever 9 at a point away from the swing shaft 8 and parallel to the swing shaft 8; a main arm shaft 14 supported by the main arm 10 at a point away from the swing shaft 8 and the lever shaft 11 and parallel to the swing shaft 8; a coil spring 16 that is mounted between the lever shaft 11 and the main arm shaft 14 and whose both mounting parts can rotate; a valve arm 18 rotating around the main arm shaft 14; and a valve body 20 coupled with the valve arm 18 and opening or closing a valve port 6.