An image forming apparatus includes a main body; a tandem type photosensitive unit, retaining photosensitive drums, mounted in the body and movable along the arrangement direction of the drums; and a developer cartridge provided for each drum, retaining a developing roller and detachably mounted on the unit. The apparatus also includes a translation member provided in the body and movable in the arrangement direction; and a link member corresponding to each cartridge and displaced to a position where a first end portion opposed to a prescribed portion of each cartridge, and a second end portion opposite to the first end portion and pressed by the translation member so the first end portion presses the prescribed portion to separate the roller from the drum and a position where the translation member is released from pressing the second end portion and the first end portion is released from pressing the prescribed portion.