To prevent the front wheel of a motor driven bicycle from floating because of steps or roughness by inputting a detecting signal from a load sensor which detects a load of the wheel of the motor driven bicycle for changing driving power of an electric motor.

A load sensor 22 which detects a load working upon a front wheel 4 is fitted at the front wheel 4 of a motor driven bicycle 2. In other words, the load sensor 22 is fitted between a front wheel shaft 24 in the front wheel 4 of the motor driven bicycle 2 and a front fork 26. The load sensor 22 mixes conductive particles in an insulated rubber which is put between two electrodes uniformly. A control means 8 inputs a detected signal from the load sensor 22, determines that a floating state occurs at the front wheel 4 at the time of no-loading when there is no conductive state between the two electrodes of the load sensor 22, cuts off or decreases rear wheel driving force, or assist force of the rear wheel 6 by an electric motor 12, weaken the forward force of the rear wheel 6, and make control so as to prevent floating state of the front wheel 4 from occurring.