A manpower actuating device for bicycles or other mechanisms is comprised of two swing levers, a sprocket wheel, a central axle, a central tube and a panel. The central axle is housed in the central tube. The sprocket wheel is fixed on the central axle. Two one-way devices are provided on the central axle. The swing lever is connected to the one-way device. A return spring is provided between the crank and the panel. The manpower actuating device is simple, convenient for use, high efficient, and of widely usage.