To provide a rotor plate capable of restraining eddy current loss by reducing the magnitude of an eddy current generated at the rotor plate.

A plurality of slits s inserted in the rotor plate 1 in a thickness direction is formed on an outer circumference side surface. Areas formed at the slits s are interposed in an outer circumference range including the outer circumference side surface of the rotor plate as an insulation body to divide the outer circumference range in a circumference direction. An eddy current path is finely divided by electrically dividing the outer circumference range with the slits s in the circumference direction in such a slit type rotor core, thus reducing the magnitude of the eddy current, and restraining the eddy current loss.