To automatically provide an appropriate supplementary power and torque at need at the time when an electrically assisted bicycle is in use.

A torque detecting rotating shaft is mounted into a five-way tube at the middle-section frame of an electrically assisted bicycle and to a transmission gear, and both ends of the rotating shaft are connected to pedals so as to be rotated at the reception of pressing on the pedals. A few signal connecting ends and rotating elements are provided for the rotating shafts, and the connecting ends are connected to one deformation amount amplifier. An electric signal of the amount of torque deformation corresponding to the rotation of the rotating shaft is outputted by the deformation amount amplifier, and traveling speed is measured by the signal. In addition, at least one signal detecting device is provided for the five-way tube, and the signal detecting device is provided with a few contact rods and one rotation detecting element, extended into the five-way tube, and brought into contact with locations corresponding to the signal connecting ends of the rotating shaft and rotating elements to detect a torque detection electric signal and rotation signal of the pedals, then the signals are transmitted to the motor power controller of the electrically assisted bicycle to control the supplementary power motor of the bicycle to output appropriate power and torque.