7B is a diagram showing an abutting position where the apparatus-side connector 34 and the developing-unit-side connector 51 b of the black developing unit 51 are in abutment against each other; FIG. 8 is a diagram showing an example of a displaying unit 95; FIG. 9A shows a table that indicates information displayable on a displaying section for when the printer 10 is used as a monochrome printer