ELECTRIC ASSIST BICYCLE

A provided electric assist bicycle can prevent an increase in the frequency of replacement of components such as a chain while achieving a satisfactory gear change, add a sufficient auxiliary driving force, prevent problems caused by interference between a mount or a battery and a front derailleur, and eliminate the need for developing a special front derailleur. A crank shaft 7a receives a human driving force transmitted from the pedal and rotates about a different axis from a motor 21. The crank shaft 7a has a human-power transmission member 29 on the outer periphery of the crank shaft 7a, the human-power transmission member 29 receiving the transmitted human driving force. The crank shaft 7a has a resultant-force transmission member 29 on the outer periphery of the crank shaft 7a, the resultant-force transmission member 29 receiving the resultant force of a human driving force and an auxiliary driving force from the motor 21. A motor drive unit 20 includes a planet gear mechanism 50 that changes a gear for the resultant force of a human driving force and an auxiliary driving force from the motor 21.