PURPOSE: To improve the deflection accuracy of a laser beam by irradiating a laser beam to a glass disc and cover glass during pressing of the cover glass to the glass disc and detecting the polarizing angle thereof.

CONSTITUTION: A glass disc 90 is horizontally positioned on a surface mating table 12. When a laser beam is irradiated from a laser tube 16, the laser beam is deflected by the disc 90 and irradiateds the surface of a scale plate 17. A photosensor S1 is moved to the position of a pinhole P with the allowance for the shift by cover glass 99 with respect to said position. The cover glass 99 on which an adhesive agent is coated is then mated onto the disc 90 and the laser beam is irradiated thereto. The operator moves the pressing position of a pressing bar 20a by operating a handle 20b in this stage to irradiate the laser beam to the position of the prescribed pinhole P, and when a photosensor S1 detects the same UV light is irradiated. The adhesive agent is cured by said light. The deflecting accuracy is thus improved.