PURPOSE: To provide a good immersion type heater having the high surface power density and the high efficiency of heat transfer in relation to an outer cylinder from a heating element.

CONSTITUTION: Electric resistance heating elements 6 are attached to a ceramic fiber-made supporting body 4 and inserted into a ceramic-made outer cylinder 2. In the heating elements 6, plate-like bodies are so bent as to be laid along the curved surface of the inner surface of the outer cylinder 2 in the longitudinal section, and zigzag current passages are formed by providing slits. A plurality of heating elements 6 are arranged in the clearance between the supporting body 4 and the outer cylinder 2 in the circumferential direction, and ceramic- made insulators 5 are arranged among respective heating elements. The heating elements are brought in surface-contact with the outer cylinder inner surface with the whole of the outer surfaces, and those outer surfaces are bonded in relation to the curved surface of the outer cylinder inner surface into an arched shape by thermal expansion in electrification and oxidization and expansion by the periodic duty.