Patent ID: 8581951

Claim:
A light scanning apparatus comprising: a light emission unit configured to emit a first light beam and a second light beam; a motor; a rotary polygon mirror configured to be rotated by the motor, periodically deflect the first light beam and the second light beam emitted from the light emission unit and form two scanning lines on a scan object; an optical sensor configured to detect the first light beam and the second light beam deflected by the rotary polygon mirror; a deviation measurement unit configured to measure a deviation amount of starting positions of the two scanning lines on the scan object in a main scanning direction, based on a first detection timing at which the optical sensor detects the first light beam and a second detection timing at which the optical sensor detects the second light beam; and a motor control unit configured to control rotation of the motor based on the second detection timing in a measurement non-execution period in which the deviation amount is not measured by the deviation measurement unit, and controls rotation of the motor without using the first detection timing that is used to measure the deviation amount, in a measurement execution period in which the deviation amount is measured by the deviation measurement unit.