An image forming device scans and exposes a photoreceptor with a luminous flux by a light scanning device, which includes a polygon mirror that deflects the luminous flux and scans the photoreceptor in a main scanning direction, a correction unit that corrects a scanning position of the luminous flux in the main scanning direction such that the scanning position of the luminous flux coincides with each reference position, and a position deviation detection unit that detects the deviation amount of the scanning position of the luminous flux in a sub scanning direction. The correction unit corrects the scanning position of the luminous flux in the main scanning direction such that a screen line with an aimed screen angle is formed by scanning with the luminous flux whose scanning position in the sub scanning direction has deviated by the deviation amount detected by the position deviation detection unit.