PURPOSE: To remove the influence of a mirror image of an object to be measured.

CONSTITUTION: This apparatus comprises a polarization irradiation device 23 for irradiating an object 21 to be measured with a polarized light 22, a polarization filter 24 for passing only linear polarized light in the specific direction, a CCD camera 26 for image-receiving light 25 reflected from the object 21 to be measured through the filter 24, and an image processor 28 for removing an image of the object to be measured of relatively weak intensity from a picture image of the CCD camera 26. The object 21 to be measured is irradiated with polarized light, and light reflected from the object 21 to be measured is image-received by the CCD camera 26 through the polarization filter 24. The image of the relatively weak intensity is removed by image processing.