Printing system, control method thereof, control apparatus, and non-transitory computer-readable storage medium

An image forming apparatus comprising:

• a printing unit configured to print an image on a sheet in accordance with a print start request;
• a creasing unit, provided downstream of the printing unit in a sheet conveyance direction, configured to crease the sheet on which the image is printed by the printing unit, the creasing unit comprising:
• a creasing die which is detachable and comprises a creasing blade;
• a die detection unit configured to detect whether or not the creasing die is attached to the creasing unit;
• a base for receiving the creasing blade;
• a sensor for detecting a sheet conveyed from the printing unit;
• and
• a pressure device for applying a pressure to the creasing die if the sensor detects the sheet, wherein when the pressure device applies the pressure to the creasing die, wherein the creasing die and the base sandwich the sheet and a crease is made on the sheet;
• a bookbinding unit, provided downstream of the creasing unit in the sheet conveyance direction, configured to perform bookbinding on the sheet on which the image is printed by the printing unit and which is creased by the creasing unit;
• a display unit;
• and
• a controller configured to determine, in accordance with receiving the print start request, whether or not the creasing die is attached to the creasing unit based on a detection result by the die detection unit, and display, if it is determined that the creasing die is not attached to the creasing unit, on the display unit, a message for prompting to attach the creasing die.