This paper proposes maximum output power control of variable-speed small wind turbine generator system. Paying attention to an optimum rotor speed of a single phase AC generator which can obtain maximum output power according to natural wind speed, the proposed method adjusts the rotor speed of the single phase AC generator to the optimum rator speed. Since this adjustment is realized on line, so that, it can be Adapted for variable-speed natural wind, a generated power brake links directly with the single phase AC generator, and the rotor speed of the single phase AC generator is adjusted by controlling a generated current that flows FET (Field-Effect Transistor) device as the generated power brake. In order to reduce heat loss of FET device, PWM (Pulse Width Modulation) control is introduced. Moreover, the experimental system for the proposed method is constituted, and the experiment is performed. Finally, the validity and the practicality of the proposed method are confirmed by experimental results.