The present invention provides a track rail mounting structure of a rectilinear guide apparatus comprising a track rail having a rotating/running surface where a plenty of rotating/running bodies rotate and run; an endless circulation route for guiding the plenty of rotating/running bodies; and a slider movably arranged with respect to the track rail via the rotating/running bodies; wherein a base where the track rail is mounted has a groove for inserting a bottom portion of the track rail, so that the bottom portion of the track rail is inserted into the groove, and a pressure member is provided for pressing at least one side surface of the track rail toward an inner side surface of the groove. As has been described above, since the pressure member is provided to press the side surface of the track rail toward the inner side surface of the groove, the side surface of the track rail is pressed by the pressure member so as to press the opposite side of the track rail to the inner side surface of the groove or both side surfaces of the track rail are pressed by the pressure member so as to be fixed to the track rail. Accordingly, even when a thermal expansion difference is caused between the track rail and the base by a temperature change, a contact portion of the pressure member slides along the side surface of the track rail so as to absorb the thermal expansion difference and accordingly, no distortion is caused in the track rail.