PURPOSE: To improve finished surface condition as well as to reduce working force by executing extension forming to the section while heating extension forming section of material to be extension formed.

CONSTITUTION: Each heater H locally heats an extension forming section Y of material to be extension formed X, that is, where the forming material X is extension formed by forming rolls 1, 2. To heat the extension forming section Y reduces the working force required for extension forming and improves finished surface condition after working. To this end, in the front and rear of each lower forming rolls 2, sensors S..., which detect the temp. before/after forming of extension forming material, are equipped. Each these temp. sensor detects the temp. of extension forming part Y of forming material X, the detected result is feeded back to each heater H. Thus, each heater H is controlled so that the extension forming part is set the prescribed temp.