To provide an assist control method for an electric power assisted bicycle capable of carrying out assist operation under predetermined conditions and effectively using an assist function without immediately stopping the assist when an output of a torque sensor is abnormal, and capable of making an operator securely recognize the abnormality of the torque sensor.

The electric power assisted bicycle comprises the torque sensor 41 for detecting a force on pedal to rotate/drive pedals, an assistance motor 42 for assisting the force on pedal, a controller for controlling a drive current of the motor 42 according to the output of the torque sensor 41, a power source switch 54 for turning on a power source of the torque sensor 41, the motor 42 and the controller. In the assist control method for the electric power assisted bicycle, when an abnormality is found in a first zero point detection value from the torque sensor 41 after turning on the power source by the power switch 54, the bicycle carries out assisted traveling in an abnormality corresponding mode where the maximum current of the motor is suppressed compared with a normal assist mode.