An image forming method which generates a video signal corresponding to an image forming command based on a video clock signal, modulates a light beam according to the video signal, and scans the modulated light beam along a main scanning direction by means of an oscillation mirror which resonates based on a drive signal, so as to form a latent image in an effective image region of a latent image carrier, the method includes: synchronizing the drive signal with the video clock signal to synchronize a detection signal with the vide clock signal, the detection signal being output from a detector which detect the light beam scanned in the main scanning direction in a region away from an effective scan region which corresponds to the effective image region; controlling a resonant frequency of the oscillation mirror based on the detection signal so that the resonant frequency of the oscillation mirror almost coincides with the frequency of the drive signal; and adjusting a position, at which the latent image is written over the latent image carrier, is adjusted by adjusting output timing of the video signal based on the detection signal from the detector.