A developing roller supplies toner to an image on an image bearing body, the image being formed in accordance with image data. A toner supplying member supplies developer material to the developer bearing member. A computing section computes a dot population density in corresponding one of a plurality of sub data areas. The plurality of sub data areas are obtained by dividing the image data such that the plurality of sub data areas are aligned in a printable area of a print medium in a direction perpendicular to the direction of travel of the print medium. A controller performs a developer material removing process based on the dot population density, in which the toner deposited on the developing roller is removed from the developing roller in an area corresponding to a low dot population density of image data.