Patent ID: 7450145

Claim:
A light beam scanner comprising: a light beam controller for controlling light emission of a light beam generating portion; a rotary polygon for deflecting and scanning the light beam; a beam detecting portion for detecting the light beam deflected by the rotary polygon; and a rotation controlling portion for controlling rotation of the rotary polygon on the basis of detection of the light beam by the beam detecting portion, wherein said light beam controller is constructed to control light emission in a selectable one of both of first and second modes; wherein in the first mode the light beam generating portion is turned ON to generate the light beam every surface period of the rotary polygon to detect the light beam; and wherein in the second mode the light beam generating portion is turned ON to generate the light beam with a long period specified with an integral multiple of 2 or more of the surface period of the rotary polygon to detect the light beam, and wherein the rotation controlling portion, during non-formation of an image, controls the rotation of the rotary polygon in the second mode.