A measuring apparatus for measuring surface topography of the slides to be measured of a guide rail is provided. The measuring apparatus includes a plurality of detecting probe and at least one moving device. The detecting probes are mounted on a probe support according to the surface topography of the slides to be measured. The moving device shifts the probe support or the slides to be measured on the cross section of the guide rail so that the detecting probe has a displacement relative to the slides to be measured. Each of the detecting probes has a corresponding coordinate system, and the corresponding coordinate system is different from each other. A standard part is utilized to correct deviations among the corresponding coordinate systems to the same coordinate system, and then the same coordinate system as a benchmark to measure the surface topography of the slides to be measured.