The image forming device of the present invention is able to be configured such that it has an image carrier that carries electrostatic latent image, a rotary type developing unit having a plurality of developing machines that stores toner in the interior thereof and is able to develop the electrostatic latent image by providing toner on the image carrier, and a control unit that is configured to execute a toner discharge process that discharges a portion of toner in the interior of a developing machine mentioned after rotating the developing unit, during a time that an image is not being formed and after a single color image formation using only a developing machine out of the plurality of developing machines.