An image forming system capable of properly managing maintenance information on a punch die mounted on a puncher. The puncher punches holes in a sheet using a removably mounted punch die. A punch die memory mounted on the punch die stores maintenance information concerning the punch die. A CPU of the image forming system detects mounting of a punch die. A RAM of the same stores maintenance information concerning each of punch dies mounted on the puncher. When a punch die is mounted on the puncher, the CPU performs comparison between maintenance information is stored in the RAM, and maintenance information stored in the punch die memory, and when the maintenance information stored in the RAM is older, the CPU updates the information in the RAM to the information in the punch die memory.