A rotational driving apparatus with a motor, a worm pressingly fitted to an output shaft of the motor, and a worm wheel meshing with the worm, is provided to output rotation of the motor from the worm wheel via the worm. The apparatus includes support, pressing, plug, and urging members. The support member is placed forming a gap with respect to a tip end of the worm, and includes a through hole positioned on a same axis as the worm. The pressing member is inserted into the through hole, and protrudes from a tip end of the through hole to butt against a tip end face of the worm. The plug member is fitted into the through hole to close the through hole, in which its fitting degree into the through hole is adjustable. The urging member is interposed between the pressing member and the plug member to urge the pressing member toward the worm.