Disclosed are an image forming apparatus capable of, and method of, improving color registration. The image forming apparatus can employ a beam deflector having a double-sided mirror portion that pivots to bi-directionally scan multiple light beams on multiple photosensitive media at different phases by using both mirror sides of the double-sided mirror portion. The individual monochromic images developed on the photosensitive media are transferred onto a transfer medium to overlap one another in phase to form a full color image.