PURPOSE: To improve the precision of the right angle of a reflective face, by fixing a polygon mirror material, where the sphere of a prescribed curvature radius is formed on one side face, and the pedestal material, where one side face is formed into a sphere complementary to the sphere above, which their spheres.

CONSTITUTION: Concave sphere 8a of curvature radius R=100W2,000mm is formed on one side face on the polygon reflective mirror material formed by the mass production system. Pedestal material 9 is provided where one side face is formed into convex sphere 9a of the same curvature radius complementary to sphere 8a and the other side face is formed into a fitting reference plane for mounting. Polygon mirror material 8 and pedestal material 9 are connected into one body with spheres 8a and 9a by an adhesive. At this time, a proper optical measuring device is used to adjust the right angle of polygon reflective face 8b to fitting reference face 9b so that declination error Δθ may be zero approximately, and they are caused to adhere to each other. Thus, polygon mirrors can be produced cheaply with the high precision of the right angle of the reflective face by the mass production system.