Abstract: An image forming apparatus of a tandem developing type is designed so that each of toners has an average circularity Cn of 0.89 or more (Cn indicates an average circularity of the toner in a developer to be transferred in the n-th time, where n is an integer of 1 to N, with N indicating the total number of colors of the toners that form an image), with C1?C2? . . . ?CN and C1<CN (where n>1) being respectively satisfied. An amorphous silicon photosensitive member is used in an image forming apparatus of the tandem developing type.