A rotary driving device includes a rotary shaft supported rotatably about
an axis thereof on a predetermined supporting member, a rotary load body
mounted on the rotary shaft to project radially outward from the rotary
shaft in such a manner that the rotary load body can rotate integrally
with the rotary shaft about the axis thereof, a driver for rotating the
rotary shaft about the axis thereof, a disk mounted on the rotary shaft
coaxially therewith for integral rotation with the rotary shaft, the disk
having a mounting hole formed therein, a pendulum loosely fitted in the
mounting hole, and an adjustment mechanism for adjusting a relative
position relationship between a central axis position of the mounting
hole and a center of gravity position of the pendulum under conditions
where the disk is rotating.