To more restrain the consumption of a battery for driving a motor, prolong a travel distance per one time charge.

This device is equipped with a pedaling force detecting means 52 equipped to a bicycle, etc., with an assist motor, traveling by rotating a driving wheel 57 by resultant force of a pedaling force FL transmitted from a crank pedal 56, and motor driving force FM transmitted from a motor 55, to detect the pedaling force FL; and a controller for drivingly control the motor 55, so that the ratio of the motor driving force FM to the pedaling force FL can be gradually increased in accordance with the increase in the pedaling force FL based on a pedaling force signal SL outputted from the detecting means 52.