An image forming apparatus is provided which makes it possible to carry out maintenance on a sheet processing apparatus connected to the image forming apparatus, by opening a cover even during operation of an image forming system comprised of the image forming apparatus and the sheet processing apparatus without detaching the sheet processing apparatus from the image forming system and moving the same and initializing the system. Settings as to post-processing on sheets are made through the operation of an operation and display unit. When any of the covers is opened, a CPU determines whether image formation and sheet conveyance are to be stopped or continued according to the settings. A controller provides control according to the result of the determination.