A plurality of halftone processing units are provided for processing each of a plurality of pieces of image data corresponding to a plurality of divided images to generate dot data representing presence or absence of dot formation. At least two halftone processing units simultaneously perform at least a part of halftone processing for at least two pieces of image data. In the halftone processing, complex error diffusion method processing of matching at least a part of dot data obtained by performing halftone processing using an error diffusion method for an error diffused gradation value of each pixel of a divided image with a determination result of a dither method, is performed.