PURPOSE: To provide a system for utilizing the brake power of a bicycle in which the power generated by a generator rotated by the transmitted rotation of wheels through brake operation is stored in a battery and utilized for illumination or as an auxiliary power at the time of running.

CONSTITUTION: Rotation of wheels is transmitted to a generator at the time of brake operation and the generated power is stored in a battery and used for illumination or as an auxiliary power. Or, the rotation of wheels is transmitted through a transmission to the generator at the time of deceleration and the generated power is stored in the battery to be utilized for illumination or as an auxiliary power. When the rotation of wheels is transmitted through a transmission to the generator, the power required for rotating the rotary shaft of generator increases as higher rotational speed of the shaft is required. Consequently, an appropriate brake power is obtained by controlling the speed change ratio.