A color printer (20) allocates all the image processing memory resource amounts to image processing on image data (GD) arranged in the main scanning direction of a print head (IH), reserves respective memory resource amounts to arranged image data (GD), and frees memory resources sequentially on completion of image processing. CPU (51) reserves an image processing memory resource for image data (1) in the storage area of RAM (53), and frees the reserved memory resource on completion of image processing on image data (1). CPU (51) repeats this processing on each element of image data contained in one print job.