Bicycle motor control system

[Object] To provide a system that can switch the operation mode of the motor in an appropriate manner. [Means] A motor control system according to the present invention comprises a communication part (72) for the motor and a first mode switching part (75). The communication part (72) for the motor is capable of performing power line communication in relation to an electrical component (12) that is mountable on a bicycle and capable of changing an operation mode of the motor. The first mode switching part (76) can be operated either by electrical power supplied via a power line (7) through which the communication part (72) performs power line communication, or by electrical power obtained from a generator (10a). The first mode switching part (75) switches the operation mode of the motor (10a), according to a state of communication with the electrical component (12), from a driving mode in which the motor is capable of assisting rotation of the bicycle wheel, to a power generating mode in which the motor outputs electrical power that has been generated using rotation of the bicycle wheel.