To lessen the height of a linear motion mechanism when the diameter of a roller is enlarged for giving a large lead to the linear motion mechanism.

A linear motion mechanism is equipped with a cogged rail 10 having a plurality of teeth 11, a roller 20c arranged at a right angle to the extending direction of the cogged rail 10 contacting with the cogged rail 10, a plate 30c supporting the roller 20c, and a plurality of eccentric shafts 40 and 41 having eccentric parts 40c and 41c arranged in a specified phase difference to be fitted to the plate 30c by these parts 40c and 41c, wherein the roller 20c is positioned between the eccentric parts 40c and 41c, and the parts 40c and 41c are made approx., equally high to the roller 20c, and thereby the height of this linear motion mechanism can be lessened even if the diameter of the roller 20c is enlarged.