Abstract: An auto-keratometer attached to an operating microscope to measure the refraction and astigmatic condition of the cornea comprises a cornea irradiating light source section disposed below the operating microscope, and switching means for selectively switching the light source section between an irradiating position on the optical axis and a retracted position. When it is desired to measure the corneal condition, the light source section is set at the irradiating position below the operating microscope, so that the light from the light source section reflected by the cornea travels through a beam splitter and is detected by a detector, whereby the refraction or astigmatic condition of the cornea is measured. If the light source section is found interfering with the operation, the light source section is set at the retracted position by rotating it through 180 degrees, whereby the working region below the microscope is widened to facilitate the operator's surgical operation on the cornea.