A light scanning apparatus makes a light beam scan along a main scanning direction on an effective scanning region having a predetermined width. A deflector includes an oscillation mirror which deflects the light beam and makes the light beam scan a second scanning range which contains but extends beyond a first scanning range corresponding to the effective scanning region A detector detects the scanning light beam which moves through a position outside the first scanning range but within the second scanning range, and outputs a detection signal A controller drives the oscillation mirror based on the detection signal and accordingly adjusts the amplitude of the oscillation mirror, and stops driving the oscillation mirror when the detection signal is not outputted from the detector even though a light source is turned on to emit the light beam.