PURPOSE: To improve controllability and to reduce vibration and noise by cutting a core material composed of an electric iron plate through wire cut electric discharge machining and forming a primary core.

CONSTITUTION: Fastening holes 3 are made through an electric iron plate 1, whereafter plural sheets of electric iron plates 1 are laminated to form a core member 7 which is then fixed temporarily. The core member 7 is clamped by side boards 11 from the opposite sides in the laminating direction and then fastened by means of bolts 13 and nuts 15. Next, the unnecessary sections of the core member 7 and the side boards 11 are cut off through wire cut electric discharge machining thus forming a primary core 17. The primary core 17 is fastened to the frame 23 of a mover 21 through bolts (not shown). Tooth surface of the primary core 17 and the right and left protrusions on the frame 23 are ground and finished. The mover 21 is used upside down, with reference to the drawing, and slides freely. Since the highly precise primary core 17 is provided, the mover 21 is operated with high controllability with reduced noise.