To simplify a work for attaching a heat generating line to housing grooves, hardly fill the housing grooves with heat even upon heating for a long time and uniformly heat a material to be heated, by pulling out both the ends of the heat generating line to the outer peripheral side of a half-split member while the heat generating line is fitted to the housing grooves 15 in a zigzag manner.

A tubular body 11 comprises a pair of half-split members 13 and 14 of circular arc shapes in section. On the inner peripheral surface of each half-split member, a plurality of rows of housing grooves 15 of a heat generating line 12 are formed at prescribed intervals. At the ends of multi-stage housing grooves 15, folded parts 17 are alternately provided. The heat generating line 12 is housed in the housing grooves 15 of each of the half-split members 13 and 14. The heat generating line 12 extends over a pair of half-split members 13 and 14 at the upper ends of the housing grooves 15 to connect the half-split members 13 and 14 together. Both the ends of the heat generating line 12 are pulled out to the outer peripheral side of each of the half-split members 13 and 14 and connected to a power source through a control device or the like. The pulled-out part is provided below the lower end position of the housing grooves 15.