PURPOSE: To form a high hardness blank by arranging a cylindrical blank inside the die forming by overlapping a conductive inductor and insulating cooling part, then performing the high frequency heating of the inductor and applying a pressure to the inner side of the blank as well, etc.

CONSTITUTION: A metal die 1 is formed by overlapping as well as winding in a coil shape the linear inductor 2 consisting of a conductive member and the linear cooling body 3 consisting of the insulating member of an alumina, etc. A hollow water passage 3a is provided on the cooling body 3 and a sensor 7 is arranged on a through hole 3b. A pipe blank 8 is arranged inside the die 1 and heated by passing a high frequency current to the inductor 2 from a high frequency generating device 5. In this case the external side of the heating part of the pipe 8 is abutted to the inner side of the die 1 and cooled and the excess bulging is checked. The sensor 7 detects the heating state, controlling the working conditions. Consequently the cylindrical blank of high hardness can be formed with a simple equipment.