Provided is an image-forming apparatus that limits reductions in image quality such as streaking even when print element discharge failure occurs in the overlap region of short heads that configure a long head. In the overlap region, among multiple overlap areas configured from rows of consecutive print elements that do not comprise print elements that have been specified as discharge failure print elements, the overlap area with the largest number of overlapping print elements is specified. When the number of print elements in said overlap area is greater than a fixed number, an overlap control for gradually changing the discharge apportionment for the fixed number of print elements in each short head is performed. Since the discharge failure of the print element is present in an area in which the short head print apportionment is 100%, the discharge failure is supplemented by, for example, increasing the discharge amounts of the adjacent print elements. But because the discharge failure of the print element is present in an area in which the short head print apportionment is 0%, supplementation is not performed.