PURPOSE: To eliminate measuring errors due to an individual difference and carry out measurement easily by such an arrangement wherein an optical means is provided so that it causes light rays reflected by the surface of the cornea to form an image between a pair of reflected images when the optical axis of an illuminating optical system becomes substantially perpendicular to the surface of the cornea.

CONSTITUTION: The reflected light rays of the corner 2 entered No. 1 image forming lens 7 enter an image sensor 9 such as CCD, etc. through No. 2 semitransparent mirror 8 which is slantly provided for their optical axis l2. As a result of this, on the surface of the sensor 9, an image of reflected litht rays of the surface and back of the cornea 2 is formed at the magnification of M1. Since the sensor 9 adjusts its focus on the surface and back of the cornea which are not within a plane perpendicular to the optical axis l2, it is slanted for the optical axis l2, by an angle of . Between No. 1 semitransparent mirror 2 and the semitransparent mirror 8, No. 2 image forming lens 10 which receives vertical reflected light rays from the surface of the cornea 2 through No. 1 semitransparent mirror 5 is arranged, and reflected light rays of the cornea 2 entered enter the sensor 9. As a result of this, reflected light rays of the cornea 2 form an image on the surface of the sensor 9 at the magnification of M2.