To provide a heat responsive steam trap capable of preventing a leakage of the steam even if a foreign material is caught between a seal surface of a valve member and a valve seat member.

A gasket 16 is provided as a seal member which tightly seals between the inner peripheral wall of a lower casing 2 and the outer periphery of a temperature control mechanical element 9. A wall member 10, a diaphragm member 11 and the valve member 13 are passed through the temperature control mechanical element 9 to form a fluid passage hole 14. A seal surface 19, which closes a lead-out passage 8 of the valve seat member 7 when the valve member 13 is seated on the valve seat member 7, is formed in the valve member 13. A bimetal 15 is provided as a temperature responsive member, which is deformed at a predetermined high temperature higher than the expansion/shrinkage temperature of an expansion medium 12 and lower than the saturation temperature so as to open the fluid passage hole 14 when the temperature is lower than the predetermined high temperature and so as to close the fluid passage hole 14 when the temperature is higher than the predetermined high temperature.