PURPOSE: To improve the efficiency of a motor by laminating a plurality of laminated layers of cores in which slots having openings and closures are alternately disposed in such a manner that the slots of different shapes are disposed adjacently.

CONSTITUTION: Cores 1 having openings 3 and closures 4 are laminated as a rotor in such a manner that slots 2 of the same shape of the cores coincide in the number of the cores corresponding to a half of the whole thickness of the whole laminated layer thereby to form a laminated core 6. Two laminated cores 6 are so laminated integrally that the slots having the openings 3 and the closures 4 are disposed adjacently thereby to form a secondary conductor. Then, since the openings 3 and the closures 4 are disposed on perpendicular lines with respect to its rotating direction without structural skew and the magnetic flux density distributions of air gaps near the openings 3 and the closures 4 are different, a skew effect due to the displacement of the magnetic flux densities can be generated.