It is possible to reduce influence of backlash effectively and to carry out precise position control even if a drive mechanism uses rotary drive of gears. For this, in moving a subject to be moved by rotation of the gears, an original point for position control is positioned by use of a sensor flag, and afterward the position control is carried out. When positioning, a bias means generates a bias in a moving direction for movement to be moved that backlash of gear drive may be removed. This sets the backlash to substantial “zero” in positioning the original point, and stabilizes an original point reset position.