An image forming apparatus is provided with a light scanning device that directs laser beams emitted from a plurality of laser light sources on to a plurality of photoconductive members via focusing device which includes optical elements and a deflecting device that deflects the beams in a main scanning direction; an image forming device which forms visible images of different colors from images written onto the photoconductive members by the light scanning device; and an intermediate transfer member or a recording sheet transport member capable of carrying the visible images formed on the photoconductive members. When in detection mode, a control device controls the correction of color registration errors between each color forms patterns on an intermediate belt by an image forming device, detects the patterns by a color registration error detection sensor, and stores the color registration error correction values obtained from the detection output of the sensor in a memory device. When forming images, the control device reads the color registration error correction values stored in the memory device, and carries out correction in accordance with the correction values via a writing start position correction device which deflects the laser position in the sub scanning direction.