Disclosed is a rotor of a generator or motor having an auxiliary coil provided around a rotor body, thereby preventing the distortion of output voltage waveforms according to the variation of load, and thereby allowing the fine adjustment of the output voltages of the generator by the control of the current flowing to the auxiliary coil. The rotor of a generator or motor includes: a rotor body adapted to axially rotate together with a rotor shaft; at least one set of N-polar and S-polar permanent magnet groups arranged along the circumferential direction of the rotor body at predetermined intervals; and a plurality of magnetic flux-increasing elements formed on the lines of magnetic force formed by the N-polar and S-polar permanent magnet groups around one side of the rotor body.