In an image forming apparatus, process cartridge, and storage medium, if an image forming stop factor occurs in a cartridge of a certain color, image forming using a cartridge of another color is enabled to increase the utilization efficiency and operability of the image forming apparatus. The image forming apparatus has a plurality of detachable process cartridges including image carriers (photosensitive drums) on which latent images are to be formed and developing units which develop the latent images. When a replacement timing for at least one of the process cartridges has arrived, only the developing unit of the process cartridge whose replacement timing has not arrived is driven in accordance with the state of the cartridge whose replacement timing has arrived to perform image forming.