PURPOSE: To improve the heat transmission efficiency of the heater by flowing a combustion gas spirally along the inner surface of a cylindrical heat transfer surface.

CONSTITUTION: A cylindrical heat transfer surface 2 is formed in the inner part of a can body 1, and a combustion gas generated by a burner 7 is passed through the inner side of the heat transfer surface 2, and other fluid is passed through a gap portion 3 formed between the can body 1 and the heat transmission surface 2. An inlet port 4 is formed on one of the heat transfer surfaces 2 and an exhaust port 5 is formed on another heat transmission surface 2. Means 6 for introducing a combustion gas or a gas is loaded in the inlet port 4 so that the working direction is directed in the tangential direction of the cylinder. When the burner 7 is loaded in the inlet port 4 and flame is sent in the heat transmission surface 1 from the tangential direction, the combustion gas G advances along the inner surface of the cylinder in a spiral flow, and exhausted through the exhaust port 5.