IMAGE FORMING SYSTEM

An image forming system includes: an image forming apparatus that forms an image on a sheet; and a post-processor including a punch unit that forms a punch hole on the sheet conveyed from the image forming apparatus, wherein the image forming apparatus includes a conveyance control part that controls conveyance of the sheet to be conveyed to the post-processor, and the punch unit includes: a perforating part that forms the punch hole on the sheet; a detection part that performs sheet side end portion detection for detecting a side end portion in a main scanning direction, and paper dust detection for detecting a paper dust amount in a detection region; a swinging part that moves the perforating part to an arbitrary position; and a hardware processor that, when a punch job is performed, controls the detection part to perform the paper dust detection.