A middle electric motor drive unit for an electric bicycle, including a motor, a controller, a sensor, a gear reducer, a one-way clutch, a chain tightener, and a housing. The middle electric motor drive unit is disposed below a frame of the electric bicycle, and in the vicinity of a pedal shaft thereof. The middle electric motor drive unit is independent from the pedal shaft with respect to functions and structure. The motor is an internal rotor and permanent magnet DC motor. The motor shaft of the motor is parallel to a gear shaft and the pedal shaft. The controller is built-in, and disposed in or on the housing. The sensor is an internal sensor or an external pedal shaft sensor.