A rotor body for an electric motor is comprised of connecting outer peripheral portions of first and second flange members made of electrically conductive material to the opposite ends of a plurality of connection members made of electrically conductive material of weak magnetic material arranged at predetermined distances therebetween in the circumferential direction with bolts and by supporting induction magnetic poles made of soft magnetic material between the connection members which are adjacent in the circumferential direction. Coupling portions of the first and second flange members and the connection member are electrically insulated by insulation coating so that an eddy current flowing in a closed circuit comprised of the first flange member, the connection member, the second flange member and the other connection member can be reduced and heat dissipation and energy loss accompanied by the eddy current can be minimized at the time of an operation.