A fitting structure for process cartridges and an image forming apparatus body of an image forming apparatus capable of fitting the process cartridges for plural colors thereto, the fitting structure including: an incompatible member with its cross-sectional shape in an axial direction being rotationally symmetrical, the incompatible member having at least one attaching projection and one displaying hole or one displaying notched portion formed on a position different from a rotational shaft of the rotationally symmetrical shape; an attached portion of the process cartridge capable of holding the incompatible member, having identification display portions for identifying the plural colors arranged on the position corresponding to the displaying hole or the displaying notched portion; and an acceptance portion of the image forming apparatus body having an acceptance concave portion for accepting the at least one attaching projection of the incompatible member.