PURPOSE: To lower the substantial magnetic flux density in an air gap so as to improve efficiency by putting a slot in the shape of U which is half open, and increasing the area of the iron opposed to the air gap.

CONSTITUTION: A plurality of U-shaped slots 3, which have half-open apertures 2 with their periphery ends half blocked from one side each, are provided at the periphery of thin round iron plate 1, and a plurality of these thin iron plates 1 are laminated to form a laminated iron core 4. And during this lamination, the slots 3 are skewed at specified inclination, and conductors 5 are inserted in the slots 3, and both ends are calked on the end ring 6 being the ring-shaped conductor, at both end faces of the laminated iron core 4, or coupled by ultrasonic bonding so as to constitute a cage rotor 7. Hereby, for the cage rotor 7 of the induction motor, the slots are in the shapes of U's being half open, so the substantial magnetic flux density in the air gap drops, and the efficiency can be improved.