To directly inspect a boundary surface between a slider and a real hard disk by compensating for influence of double refraction created by a stress pattern of a glass disk that rotates at a high speed.

There are disclosed a device and a method for measuring and compensating for double refraction in a rotating abrasion glass disk 2 used for an optical floating height tester utilizing polarization. A polarized light 1, 3 is projected to an upper surface 24 of a disk 20 and is refracted to pass through the disk 20. It reaches a measuring point 90 on the opposite surface 25, reflected thereat to pass through the disk 20 and refracted to go out from the disk 20. It becomes a light beam 9 including a and p polarizations. A difference of phase between s and p polarzations is measured and detected by a phase detector 13. The variation of a phase θG with respect to the position determined by the measuring position provides double refraction parameters bp, bo on the disk 20. The phase detector 13 measures the phase θG at an inclination angleξ determined in an incident plane 101 which is determined by an incident ray 3 and an exit ray 9 drown by lines passing through the measuring point 90 perpendicular to a radius line 102 of the disk 20.