To provide a disc type steam trap in which a structure is simplified.

A pressure changing chamber 4 in communication with an inlet 2 and an outlet 3 of a body 1 is formed of lid member 5 and the body 1. An inner ring valve seat 6 and an outer ring valve seat 7 are formed in a cocentric shape in the opening end of the side of the pressure changing chamber 4 of the inlet 2 and the outlet 3 and an annular groove 8 is formed between them. A valve disc 11 separating from and sitting on the upper end of the inner and outer valve seats 6, 7 is arranged in the pressure changing chamber 4. The valve disc 11 is formed of a disc-shape bimetal. The valve disc 11 formed of the bimetal is inverted upward convexly and discharges low temperature condensed water or low temperature air outside of a system from the outlet 3 when the low temperature air or the low temperature condensed water flows into the pressure changing chamber 4 from the inlet 2. The valve disc 11 is inverted downward convexly and sits on the inner and outer valve seats 6, 7 and prevents the discharge of high temperature steam when the high temperature steam or the high temperature condensed water flows in, and is separated from the valve seats and discharges only the condensed water to the outlet 3 when the high temperature condensed water flows in.