A rotor for a dynamo-electric machine is capable of reducing core loss in a field core, and thus increasing the output efficiency. A rotor for a vehicular AC generator in accordance with the present invention is equipped with: a rotor coil through which current flows to generate magnetic flux; a field core which is provided such that it covers the rotor coil and which is composed of a first field core member and a second field core member having triangular magnetic poles, respectively; and an inter-magnetic-pole member which is provided between adjacent triangular magnetic poles and which has been magnetized in a direction so as to reduce the leakage of magnetic flux between the triangular magnetic poles and; wherein the triangular magnetic poles are constructed by laminating thin steel plates to reduce core loss.