PURPOSE: To smoothly bend a tube to a prescribed shape by moving a movable electrode to the side along a prescribed course to a lengthwise axial line.

CONSTITUTION: When a holding electrode 11 and the movable electrode 15 are energized electrically through a control circuit 21 and a transformer 20, the area between both electrodes 11, 15 is subjected to red-heating. At this time, when the rear part of the tube 10 is advanced by advancing a holding means 22, the movable electrode 15 moves along a circular arc revolving round the center 19 of revolution and to a side position to a lengthwise axial line A. As a result, the tube 10 is bent at a red-heated area 29 and a part of the tube 10 in the front direction from this area displaces to the side to the lengthwise axial line A. After and before a bending operation ends, when refrigeration medium of high pressure is sent to a passage 27 of cooling means 26, it is ejected from a nozzle opening 28 to the internal circumferential surface of the tube 10 and the red-heated and bent area 29 is cooled nearly to the room temperature.