A drum unit of an image forming apparatus including a flange that is integrally provided with the photoconductor drum. A frame rotatably supports the photoconductor drum and covers its side. A gear portion is integrally formed with an outer circumferential surface of the flange. An outer diameter of the gear portion is larger than a diameter size of the photoconductor drum. A guide member is provided on an upper surface of the frame and guides the edge portion upward when the drum unit is pulled out of the apparatus main body. An upper surface of the guide member includes first and second guide surfaces. The first guide surface is located more on a side of a center of the photoconductor drum than the edge position, and the second guide surface is located more on the side of the insertion direction than the edge position.