To provide a power generator for activating a generator to generate power by using a rotational force of one side of left and right driving wheels to which a motive force is transmitted through a differential gear of an automobile, configured to be safe without any movement of a vehicle during power generation, high in power generation efficiency, and low in cost.

A recess is formed to fit a wheel nut of a driving wheel 3 in the inner surface of a base plate 5 to be loaded on a one-side driving wheel 3. A plurality of clamps 5e are formed in the peripheral part of the base plate 5, which are hooked in the tire of the driving wheel 3 to press the base plate 5 into contact with the driving wheel 3. An output shaft 5b is projected in the outer peripheral center of the base plate 5, the end of the output shaft 5b is connected to one of free joints 6, and the other of the free joints 6 is connected to the rotary shaft 7a of a generator 7 via a speed-up gear 9. A vehicle body is jacked up to cause the driving wheel 3 of one side to float, the other wheel is fixed by a wheel stopper, and the base plate 5 is fixed to the floating driving wheel 3 to rotate the driving wheel 3.