PURPOSE: To effectively utilize extreme outside circumference silicon steel plates by a method wherein respective cutoff sections of a belt-shaped extreme outside circumference silicon steel plate formed the cutoff sections and connection sections at opposite end sections respectively by slits notched in the longitudinal direction are welded.

CONSTITUTION: Cutoff sections 1c, 1d and connection sections 1e, 1f are formed by forming slits 1a, 1b notched in the longitudinal direction respectively at the opposite end sections of an extreme outside circumference silicon steel plate 1. Respective cutoff sections 1c, 1d are welded by rolling the steel plate 1. Next, a plurality of silicon steel plates 2 are stacked in the inside of the ring steel plate 1 to form a wound core. After formation and annealing, a spot welding section B is removed to cutdown the cutoff sections 1c, 1d. Next, both end sections A of the steel plates 1, 2 are opened to insert windings 3 in the steel plates 1, 2 and both the end sections A are faced again. After that, spot welding is applied to respective connection sections 1e, 1f of the steel plate 1 to clamp the steel plate 2.