PURPOSE: To facilitate the forming of the cylindrical blank of high hardness and to improve the versatility of the device by arranging in a line plural inductor serving a die member as well consisting of a conductive material and bulging by passing a high frequency current selectively to respective inductor.

CONSTITUTION: A metal die 1 is composed by arranging in a line plural die members 2a, 2b, 2c, 2d. In this case the die member 2 is formed by coiling the linear inductor consisting of a conductive material in a coil shape and so that its coiling part is not abutted each other. A blank pipe 3 is arranged inside th die 1, a high frequency current is passed by selecting the linear inductor by a high frequency generating device 4 and the inner pressure is applied by a pressure increaser with heating the pipe 3. The part of the pipe 3 selectively heated is bulged and the excess bulging is checked by the inner face of the die 2. In this way the forming of the blank 3 of high hardness is made easy and the versatility of the device is improved.