An image forming apparatus having a photosensitive element, is provided with a light source for scanning light to the photosensitive element; a light blocking member disposed in a light traveling path of the light from the light source and moving between a blocking position where the light blocking member blocks the light scanned from the light source and a withdrawal position where the light blocking member is withdrawn from the blocking position; a power supply unit for supplying electric power to the light source for scanning light; a power switch unit for regulating power supply from the power supply unit; and an operating part locating the light blocking member at the blocking position and controlling the power switch unit to cut off the power supply in a predetermined exposure condition. As a result, a user is kept from being exposed to the light from a light source.