There is provided a mounting tool, for a linear displacement measuring apparatus, which is capable of reducing thermal stress of a scale housing case and is detachable while having a simple structure.The mounting tool includes a cylindrical bush inserted into a through hole drilled in the scale housing case, an O-ring interposed between an inside wall of the through hole and the bush, a mounting screw inserted into a cylindrical hole of the bush and screwed into a mounting face, and a plate spring arranged between a head part of the mounting screw and an outside face of the scale housing case, and biasing the scale housing case toward the mounting face.