An elastic member (91) for urging a developer carrier (39) in the direction of an image carrier (31) is located in a casing (36) of a developer cartridge (24). Since the elastic member (91) will be new whenever the developer cartridge (24) is replaced, an urging force of the elastic member (91) will not deteriorate over time. Thus, a proper pressing state of the developer carrier (39) on the imagecarrier (31) is maintained. Thus, the amount of toner supplied from the developer carrier (39) to the image carrier (31) is stable. Thereby, a picture of high quality can be formed continuously without poor development by poor pressure between the developer carrier (39) and the image carrier(31).