To provide a steam trap provided with automatic blowing mechanism for pressure and air in the trap.

In this steam trap, an inlet 4, a valve chamber 3 and an outlet 6 are formed by a casing formed of a body 1 and a cover 2. A drain valve hole 16 for communicating the valve chamber 3 with the outlet 6 is provided at the lower part of the valve chamber 3, and a float 17 for opening/closing the drain valve hole 16 is accommodated in the valve chamber 3. In a steam trap of such constitution, bimetal 12 partitioning the valve chamber 3 from the outlet side is fitted to the lower part of the valve chamber 3 by a bolt 13 serving also as a stopper, and a drain valve hole is formed in the bimetal 12. Until pressure in the valve chamber 3 reaches the maximum working pressure, the drain valve hole is retreated from the position, opened/closed by the float, at the time of low temperature by the deforming action of the bimetal, and the drain valve hole is advanced into the position, opened/closed by the float, at the time of high temperature. When the pressure in the valve chamber becomes the maximum working pressure or higher, the bimetal is forcibly deformed to retreat the drain valve hole from the position opened/closed by the float.