To provide a float type drain trap which can extend the period before clogging of a filter.

A lid body 2 is fastened to a body 1 having an inlet 4 and an outlet 6 to form a casing having a valve chamber 3 inside. A valve seat 9 having a valve hole 7 is connected to the lid body 2 on the lower side wall of the valve chamber 3. A hollowed sphere-like sealed float 11 for opening and closing the valve hole 7 is disposed within the valve chamber 3 in a free state. A foreign matter capturing cap-like filter 15 is disposed above the float 11 in the valve chamber 3, and a holding cylinder 16 placed on the lid body 2 is disposed to hold the filter 15 around the float 11. The filter 15 has a number of filtering holes smaller in diameter than the valve hole 7. The upstream side of the float 11 is allowed to communicate with the inlet 4 through the filter 15. A foreign matter collecting space 17 is formed between the outside of the holding cylinder 16 below the filter 15 and the inner side of the cap body 2.