To provide a tandem type photoreceptor unit for highly precisely positioning a photoreceptor drum, and to provide an image forming apparatus with the tandem type photoreceptor unit.

A drum supporting hole 32 is formed on a first inside plate 24 of a drum unit 4. A first bearing member 90 is fit in the drum supporting hole 32. The right end of the photoreceptor drum 5 is supported by the first inside plate 24 through the first bearing member 90. The drum supporting hole 32 includes four linear parts 60 on its inner surface. The four linear parts 60 come into contact with a virtual circle 62 virtually set in the drum supporting hole 32, and are arranged at equal angle intervals relative to a center of the virtual circle 62. Meanwhile, the first bearing member 90 includes a cylindrical part 92 inserted in the drum supporting hole 32. The cylindrical part 92 includes an outer peripheral surface whose outside diameter is larger than the diameter of the virtual circle 62 virtually set in the drum supporting hole 32.

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