PURPOSE: To enhance the concentricity of a coil to a roter and make the rotary speed control into high precision by setting a base, having conductive layer to a laser beam machine, forming a coil for a generator and cutting a mounting hole.

CONSTITUTION: A laser beam is emitted from a laser emission nozzle 21 while a base 19 is setted on the table and a laser emission nozzle 21 is moved against the base 19 by vertically and horizontally movement of the table. A round mounting hole 18 is cut in the center of the base 19, a conductive layer 23 of the base 19 is only cut into two vertical grooves each other by the same pattern of the coil for frequency generating and the coil for frequency generating is formed between the cut parts 24, 25.