To provide a disk type steam trap with a long working life by preventing foreign substances from entering the periphery of a bimetal.

A variable pressure chamber 3 is formed inside a body 1 having an inlet 4 and an outlet 5 by fixing a lid 2 to the body 1. A jet hole 6 opened at the center of the variable pressure chamber 3 is provided to communicate an inlet 4 with the variable pressure chamber 3. An annular groove 8 opened at the outer circumference of a jet hole 6 is formed. While an inner ring valve seat 9 is formed between the jet hole 6 and the annular groove 8, an outer ring valve seat 10 is formed to the outer circumference of the annular groove 8. A discharge hole 7 is provided from the annular groove 8 to communicate the variable pressure chamber 3 with the outlet 5. A disk-like valve disk 11 which sits on or separates from the inner ring valve seat 9 and the outer ring valve seat 10, is arranged in the variable pressure chamber 3. A guide rod 15 is fit on the top of the valve disk 11, and is brought into contact with a bimetal 19. A foreign substance such as iron rust are less likely to flow into a bimetal chamber 17, to thereby attain a long life disk type steam trap.