PURPOSE: To obtain a disk type steam trap in which an outlet passage is not reduced nor clogged by the accumulation of foreign matter.

CONSTITUTION: A check valve seat 14 is formed at the outlet 11 end of an outlet passage 10. A rolling member 15 in positioned freely in the outlet passage 10. The rolling member 15 comprises two bar materials 16 and 17 of which upper ends are positioned in an annular groove 6 and a check valve body 18 which is installed at the lower end of the bar materials 16 and 17 and opens and closes the check valve seat 14. The bar materials 16 and 17 are rolled by exhausted fluid to prevent foreign matter from adhering at the top section, and the check valve body 18 seats on the check valve seat 14 in reverse flow to prevent foreign matter from flowing back to the outlet passage 10.