Assisting force control device for bicycle

An assisting force control device for use in a bicycle with an electric motor and a crankshaft (11) includes a driving member (2) coupled co-rotatably to the crankshaft (11), a strain sensor (4) disposed on the driving member (2), a torque calculation unit (5) coupled to the strain sensor (4) for calculating and outputting a torque signal (93), a rotational speed detection unit (7) mounted on the crankshaft (11) for outputting a rotational speed detecting signal (96), and a control unit (8). The control unit (8) includes a receiving module (81) for receiving the rotational speed detecting signal (96) and the torque signal (93), and a processing module (82) coupled to the receiving module (81) for generating a force control signal (97) to control the electric motor accordingly.