There is provided an image forming apparatus including a main casing, an opening-closing member configured to open and close an opening on a side of the main casing and to move between an open position and a closed position, a belt unit configured to move between a first position and a second position, a drum unit configured to move between a third position and a fourth position, a developing device unit configured to move in an arrangement direction of developing rollers, and an interlock mechanism configured such that in response to a movement of the opening-closing member from the closed position to the open position, the belt unit moves from the first position to the second position and the drum unit moves from the third position to the fourth position.