When a halftone image region that is below a predetermined density is to be reproduced, a processing unit controlling an exposure unit selects an exposure pattern that can represent a record dot diameter within a range based on a predetermined rule from exposure patterns prepared in advance. Accordingly, graininess is suppressed. When there are a plurality of exposure patterns that can be applied, the exposure pattern with the lowest number of dots present per 1 inch is employed. Accordingly, a halftone image is formed with the image reproducibility improved.