A light scanning apparatus makes a light beam scan along a main scanning direction on an effective scanning region which has a predetermined width. The apparatus comprises: a light source which emits the light beam; a deflector which includes an oscillation mirror which oscillates about an oscillatory axis which is orthogonal or approximately orthogonal to the main scanning direction, deflects the light beam emitted from the light source using the oscillation mirror, and makes the light beam scan a second scanning range which contains but extends beyond a first scanning range which corresponds to the effective scanning region; a detector which detects the scanning light beam which moves through a position which is outside the first scanning range but is within the second scanning range, and outputs a signal; and a controller which controls a mirror drive signal fed to the oscillation mirror based on the output signal from the detector and accordingly adjusts the amplitude of the oscillation mirror. In the apparatus above, the controller stops driving the oscillation mirror when confirming based on the output signal that the oscillation mirror is under abnormal control.