An isolation point counting section, an internal edge counting section, and a continuity detecting section are provided at a halftone dot internal character region signal generating section. The halftone dot internal character region signal generating section discriminates a character region in a halftone dot image based on the detection results of the isolation point counting value caused by the isolation point counting section, the internal edge count value caused by the internal edge counting section, and the presence or absence of continuity of the internal edges caused by the continuity detecting section by making best use of the fact that the halftone dot region and character region in the halftone dot image are completely reversed in their characteristics.