A rack includes a first member including a main tooth, a second member including an opposite tooth disposed opposite the main tooth, the second member being rotatable with respect to the first member, a first forcing unit configured to force the main tooth, and a second forcing unit configured to force the main tooth and the opposite tooth closer to each other. On a plane perpendicular to a central axis of a lead screw, each of a part at which the first forcing unit forces the first member, a part at which the second forcing unit forces the first member, and a part at which the second forcing unit forces the second member is disposed on a movable member side with respect to a straight line connecting a rotating axis of the second member and the central axis.