To ensure exact positioning and power transmission wherever a carriage part is located by keeping a belt deformation amount constant.

A rack part is arranged on a surface of a movable member 1 which is movable in a longitudinal direction, and a pair of guide members 4 are arranged with a clearance with the movable member 1. A cogged belt 3 is arranged on the rack part side of the movable member 1 and meshes with the rack part between a guide member 4 and the end of the movable member 1. A curved part 3a where the cogged belt 3 does not mesh with the rack part is arranged between both the guide members 4 and the cogged belt 3 meshes with a drive sprocket 2 in the curved part 3a.