A linear encoder for numeric-control machine tools is provided that includes: a substantially rectilinear section-bar, which is adapted to be fixed on the structure of the machine tool; a substantially rectilinear scale strip, which is fixed on the section-bar so as to extend along the section-bar parallel to the section-bar longitudinal axis; a movable slider which is fitted/mounted on the section-bar so as to be able to move along the section-bar parallel to the section-bar longitudinal axis and skimming the scale strip, and which is adapted to be rigidly fixed to the movable piece of the machine tool; an electronic reading apparatus which is at least partially placed aboard the movable slider and is adapted to read the position of the movable slider on the scale strip; and a thermal-stabilization device which is adapted to bring and maintain substantially the whole scale strip stably at a predetermined target temperature.