A coordinate measuring instrument wherein a measuring element is supported through a measuring element support member in a manner to be displaceable relative to the upper surface of a bedplate in directions of X, Y and Z axes perpendicularly intersecting one another, and a shape and the like of a workpiece to be measured are measured from displacements of the measuring element. This coordinate measuring instrument is provided with a guide rail projecting from one side of the bedplate, for guiding the measuring element support member in the direction of the Y axis and the upper surface of this guide rail is disposed in parallel to the upper surface of the bedplate.