To enable insertion into a motor housing without fastening fellow core blocks by welding or bonding and to fix them in both directions in all of the circumferential direction, the radial direction, and the axial direction of a motor by only the simple engagement of adjacent core blocks.

The core block has an arm and a yoke extending to both sides in its circumferential direction from the end of the arm, and at least the yoke is constituted as a multi-stage core by piling up cores in the axial direction or in the radial direction of a motor rotating shaft. For core blocks, an engaging part for coupling core blocks with each other is formed at both ends of the yoke, and this engaging part includes protrusions which extend in its circumferential direction from both ends of the yoke in the first stage core, and besides it includes recesses which are juxtaposed in the radial direction of the protrusions so as to accommodate the protrusions of adjacent core blocks. The second stage core is provided with protrusions and recesses in positions that are radially reverse to the protrusions and recesses.