An image forming apparatus includes an image forming assembly including an image carrier including a support portion and a developing device including a projecting portion, an image forming apparatus body including a frame and an assembly covering member that rotates between a closed state and an open state and that has a support hole for receiving the support portion and an interference avoiding hole for receiving the projecting portion, and a vibration reducing member. The vibration reducing member reduces vibration of the developing device relative to the image carrier by being fitted in a gap around the projecting portion in the interference avoiding hole in the state in which the projecting portion is inserted in the interference avoiding hole in the assembly covering member in the closed state. The image forming apparatus is operated in the state in which the vibration reducing member is removed.