An image forming apparatus for forming a color image has developing devices with different color toners. Each developing device has a toner carrier and a layer thickness-controller facing the carrier. Circularity of toner in a particular color is smaller than that of toners in other colors. The layer thickness-controllers of the developing devices containing toners in other colors contact the carrier at a particular linear pressure. Additionally, the coefficient of variance (CV value) of the particle diameter distribution of toner in a particular color may be defined by the formula CV ⁢ ⁢ VALUE = ( STANDARD ⁢ ⁢ DEVIATION ⁢ ⁢ OF ⁢ ⁢ VOLUME - AVERAGE ⁢ ⁢ PARTICLE ⁢ ⁢ DIAMETER ⁢ ⁢ DISTRIBUTION ) ( ARITHMETIC ⁢ ⁢ VOLUME ⁢ - AVERAGE ⁢ ⁢ PARTICLE ⁢ ⁢ DIAMETER ) × 100 and may exceed the CV value of the toners in other colors. The image forming apparatus contains the contaminating toner in the developing device, makes the image resistant to color mixing, and reduces image staining, even if there is leakage of a toner and contamination of the toners in different colors with the scattered toner.