To provide a bicycle with an inexpensive auxiliary power device having a simple structure in which it is unnecessary to provide any exclusive bicycle, and capable of reducing the number of component to be individually mounted, and to provide an auxiliary power device unit capable of easily post-fitting an auxiliary power device.

There are provided a first chain sprocket mechanism 21 for transmitting the force between a crank shaft 3 and an intermediate shaft 11 by providing the intermediate shaft 11 between and in parallel with the crank shaft 3 and a rear axle 5 of a bicycle 1, and a second chain sprocket mechanism 27 for transmitting the force between the intermediate shaft 11 and the rear axle 5. A drive motor 9 is constituted with the intermediate shaft 11 as a motor shaft. The torque of the intermediate shaft 11 is detected by a torque detection means 33. The output of the drive motor 9 is controlled by the detected torque value.