Energy-saving chain-gear of bicycle

The utility model relates to a bicycle labor saving sprocket, which makes pedal change applying force variation in rotary process. The middle axis of the bicycle is provided with an ellipse shape sprocket (3). Due to adopting the ellipse shape bicycle middle axis sprocket which is a non-equalization diameter gear, i.e. the forced arm is variable, thus in installation process, relative change of applying force arm is considered, i.e. if the applying force arm is small, the applying force arm is small, if the applying force arm is large, the relative applying force arm is large, which can make the rider save labor under reaching same speed.