An image forming apparatus that senses image position differences without a dedicated light source or driver circuit, the apparatus including a transfer belt and an image forming unit for deflecting a light emitted from a light source, forming a latent image on a surface by scanning the deflected light, developing the latent image, and transferring the developed image onto the belt or recording medium delivered by the belt. The apparatus also includes an optical path changing unit for changing an optical path of the light before it reaches the deflecting unit and guiding the light to a sensing position of a sensing image formed on the surface of the transfer belt, a sensing unit for receiving a light reflected or transmitted by the sensing position and sensing the sensing image, and a control unit for controlling the image forming unit according to the sensing signal sensed by the sensing unit.