PURPOSE: To prevent a reflecting position from being deviated due to an angle of rotation by forming a sheet of plane mirror by adhering the mirror coating with each other for two sheets of plane mirrors to only one plane to which the mirror coating is applied.

CONSTITUTION: The two sheets of plane mirrors are generated by applying the mirror coating 12a, 12b on one plane of glass 11a, 11b, respectively, and the mirror coating 12a, 12b of those mirrors are adhered with each other by facing them back to back, then, a sheet of mirror for optical scan can be prepared. A rotary shaft 13 is provided as required.