PURPOSE: To reduce loss of a material, and to elevate working efficiency, by detecting a temperature variation caused by a structure variation of a material to be worked, raising a temperature by a prescribed temperature from the detected temperature, and executing plastic working.

CONSTITUTION: In case of manufacturing a tapered rod, a material to be worked 1 is electrified and heated by a heating electric power suply 6, and its temperature variation is measured by a detector 12. When a temperature variation rate is suddenly changed due to a sudden change of a structure variation of the material to be worked 1, a command is given to the electric power supply 6 from an optimum working temperature controlling circuit 14 so that a temperature becomes higher than the detected temperature by a prescribed temperature. In this rgard, the prescribed temperature is set by a quality, dimensions, etc. of the material to be worked 1. When the material to be worked 1 has been heated to a state that its plasticity is highest, the material to be worked 1 is sprayed with cooling gas from nozzles 11 of air nozzle blocks 7, 8 and 9, is made to have a prescribed temperature pattern toward its axial direction, is drawn in the axial direction by moving a drawing chuck 3, and a tapered rod having different diameter parts (a), (b) and (c) is molded.