Abstract: This invention relates to a rotary driving device, wherein a rotation and an axial movement of an input shaft are imparted to intermediate members as a rotary movement through a torsional connection, whereby the rotary movement of the intermediate members is imparted to an output shaft through a clutch mechanism. This rotary driving device can be used as a driving device in a bicycle for example. Without utilizing the conventional device wherein a chain, a sprocket and the like are used, a rocking movement of a pair of rocking arms connected to the input shaft makes it possible to advance the bicycle.