To provide a rotary driving device which achieves generation of rotational force with the use of eccentric rotation of a rotary body and a high efficiency of rotary driving motion.

The rotary driving device 1 comprises: a core gear 2 positioned in the center; four sets of rotary bodies 3R, 3L, 3U and 3D externally brought into contact with the core gear 2 at four equidistant points; and a rolling element 4 internally brought into contact with the rotary bodies 3R, 3L, 3U and 3D while having an eccentric position of the center of gravity. The position of the center of gravity of the rotary driving device 1 is always eccentric with respect to a pivot 6 which is a rotation center.