A motor-assisted bicycle, on which a motor-driven assist unit including a crank shaft and a motor for generating assist-power to be imparted to the crank shaft is mounted, has a downwardly projecting U-shaped body frame connected to a head pipe. The motor is positioned rearwardly from the crank shaft; and the bottom of the U-shaped body frame is positioned forwardly from the unit and is also positioned under the crank shaft. Since the bottom, that is, the lowermost portion of the U-shaped body frame can be lowered, the position of the obstacle to the rider's motion to get on and off the bicycle becomes lower, with a result that it is easy for the rider to stride across the U-shaped body frame, thereby improving the usability of the bicycle when the rider gets on and off the bicycle. |