Apparatus using a rotating polygon to form an image, the apparatus determining the polygon rotates stably at a predetermined rotation number

摘要

An image forming apparatus includes a light beam generator for generating a light beam, a rotational polygon mirror for scanning the light beam generated by the light beam generator across a member to be illuminated, a rotation detector for detecting whether or not the rotational polygon mirror rotates at a predetermined rotation number for an image formation, and a determining device for determining whether or not the rotational polygon mirror rotates at the predetermined rotation number stably in accordance with an output from the rotation detector.