To assure the parallelism of the axial center of a photoreceptor drum 110 relative to the axial centers of a resist roller 510, and fixing rollers 517a and 517b.

In a printer 500, a drum unit 100 has a drum drive shaft 108 and a photoreceptor drum 110. A positioning member 10 having a positioning cylindrical part 12 and a positioning hole 13 is disposed on a main body rear wall 522. A unit rear wall 104 is provided with a holding cylindrical part 112. A drum drive gear 570 is supported in the positioning hole 13 of the positioning member 10. In the drum unit 100, the holding cylindrical part 112 of the unit rear wall 104 is supported by the positioning cylindrical part 12 of the positioning member 10. The drum drive shaft 108 and a drum drive gear 570 are connected by couplings 114 and 580.

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