An image forming apparatus includes a photoreceptor allowing an electrostatic latent image to be formed by light exposure, a light source emitting light beams, a light deflecting device for deflecting light beams from the light source, an exposure controlling device for controlling deflecting actions of the deflecting device, and an image-forming optical device receiving light beams deflected by the light deflecting device and image-forming the light beams on the photoreceptor so as to create a latent image composed of a plurality of pixels thereon. In the configuration, the light deflecting device includes a micro-mirror array device which is composed of a multiple number of mirror facet elements arranged matrix-wise, in two-dimensions, and which is disposed so that each row of the mirror facet elements extends in parallel with the rotating axis of the photoreceptor and normals of the mirror facet elements are substantially perpendicular to the rotating axis of the photoreceptor. Each of the mirror facet elements in a single column can individually be controlled to be oriented at any angle to simultaneously deflect light to the same location on the photoreceptor to vary density of the image formed thereon.