PURPOSE: To reduce assembling man-hour by forming an iron core block through bonding of a plurality of its multiples of the magnetic plates having the same width.

CONSTITUTION: A plurality of magnetic plates 1aW4a, which are cut into the predetermined shape in such widths different to each other stepwise, are stacked forming several groups consisting of several plates in the same width. These plates are bonded except for the areas near the bonding surface at the end portions of longitudinal direction. Thereby, iron core blocks 1bW4b are formed. Meanwhile, a plurality of magnetic plates are stacked for every multiple and bonded in order to form other iron core block wherein the junction areas of edge portions in the longitudinal direction are shifted alternately in every plurality of plates as much as the entrance dimension. The stages 1W4 are formed by stacking the blocks having the equal width. The leg portions 41W43 of iron core and upper and lower two yokes 44, 45 are inter-connected each other with a connecting angle of 45° while the junction surface 46 in the longitudinal direction of the magnetic plate is shifted each other in a plurality of plates. With such a structure, reassembling of iron core can be realized only with stacking of the iron core blocks. Accordingly, the iron core can be assembled easily and assembling man hour can also be saved.