An apparatus includes a driver configured to rotate a lead screw, a rack unit including a mated portion mated with the lead screw, the rack unit being coupled with the holder and configured to move along the lead screw as the lead screw is rotated by the driver, a first elastic member configured to force the mated portion against the lead screw with a first force F1, an opposed cog arranged opposite to the mated portion with respect to the lead screw and displaceable relative to the mated portion, and a second elastic unit configured force the opposed cog unit with a second force F2 toward the lead screw. F1