A control part provides a first region in which an image is formed on an image carrier using only a dark-color toner. The control part provides a second region, which is adjacent to the first region, in which an image is formed using a dark-color toner and a light-color toner. The control part provides a third region in which an image is formed using only a light-color toner at the boundary of the first and second regions. The control part controls a latent-image forming unit, a light-color developing unit and a dark-color developing unit so as to form an image in which these regions are provided. The control part may provide a third region in which neither a light-color toner nor a dark-color toner is used at the boundary of the first and second regions.