A light scanning apparatus includes: a light emission unit emitting a first light beam and a second light beam; a motor; a rotary polygon mirror rotated by the motor, forming two scanning lines on a scan object at the same time; an optical sensor detecting the first light beam and the second light beam deflected by the rotary polygon mirror; a deviation measurement unit measuring a deviation amount of starting positions of the two scanning lines on the scan object 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 controlling rotation of the motor based on the second detection timing in a measurement non-execution period, and controls rotation of the motor without using the first detection timing in a measurement execution period.