An image forming apparatus may include a main body, an endless belt, and a drum unit. The drum unit may support a black photosensitive drum and color photosensitive drums in a mounting direction. The black photosensitive drum may include a first axis in an axial direction perpendicular to the mounting direction. Each color photosensitive drum may have a second axis extending parallel to the axial direction. The black photosensitive drum may be disposed at a position nearest to a first end of the drum unit. A second end of the drum unit may be pivotable about the first axis between initial and pivot positions. The photosensitive drums contact the endless belt when the drum unit is in the initial position. The black photosensitive drum contacts the endless belt and the color photosensitive drums are separated from the endless belt when the drum unit is in the pivot position.