To provide a float type steam trap capable of surely cleaning off foreign matter adhering to an inner surface of a valve hole.

An inlet 2, a valve chest 3 and an outlet 4 are formed in a casing 1. The valve chest 3 is integrally formed of a hollow spherical ball-like member 5. A valve seat member 7 with the valve hole 6 is disposed in the valve chest 3 formed of the ball-like member 5. A float 8 is disposed in a free state in a position to face the valve seat member 7. A cylindrical screen 10 is attached to the outer peripheries of the float 8 and a support plate 9. The ball-like member 5 is provided with a plurality of through-holes 12 and 13. The ball-like member 5 is rotated; the through-hole 12 is rotated to a position to face an exhaust port 11; and the valve hole 6 is rotated to a position to face the inlet 2, namely, a position in which the through-hole 13 is indicated in Fig.1. Thus, a mixed fluid flowing in from the inlet 2 flows back through the valve hole 6 and performs cleaning.