PURPOSE: To directly, speedily, and surely inspect the presence or absence of a birefringence part without any contact by detecting light component through a polarization plate at the light-reception means side of a plastic lens which is retained between cross polarization plates.

CONSTITUTION: A plastic lens 3 is positioned and retained between crossing polarization plates 4 in the polarization direction of a polarization plate 2 to pick up an image with a CCD camera 5. When no birefringence part 16 is generated at the lens 3, light at a non-polarization light source 1 is completely shielded. However, when the refraction part 16 is generated, light component in the polarization direction of an inner polarization plate 4 of light through the refraction part 16 passes through the polarization plate 4 and the image is picked up by a camera 5. An image corresponding to the refraction part 16 is subjected to image processing by a processor 7 for upper image processing for binary-coding. At this time, the outer-periphery image of the lens 3 is subjected to image processing. In the image processing, the difference image between the binary-coded image and the outer-periphery image is obtained and the position of the refraction part 16 on the lens 3 is specified based on the difference image, thus obtaining the angle to the center of the lens 3.