Abstract: A concentricity evaluating system has a stage supported by a hydrostatic bearing in at least one of radial and thrust directions. The angle of rotation of the stage is detected by a rotation angle detector. On the stage a hollow cylindrical member is fixed coaxially. Onto the upper end face of the hollow cylindrical member or into the hole thereof a light beam is applied from a light emitting means, whereby a clear image of the profile of the hole is formed. The image thus formed is enlarged by an optical system. The light beam passing through the optical system reaches a photodiode array which is positioned across a part of the enlarged image. The hollow cylindrical member is rotated, and a displacement meter is detected how the circumference of the hollow cylindrical member varies as the member rotates. Data from the displacement meter, photodiode array and the rotation angle detector are fed to an interface and processed.