Image forming system, sheet treating apparatus, image forming apparatus, control program and storage medium

An image forming system comprising:

• a sheet conveying path on which a sheet is conveyed, the sheet having a side edge substantially parallel to the direction of conveyance;
• an image forming unit which forms an image on the sheet conveyed on the sheet conveying path;
• a punching member which effects punching on the sheet conveyed on the sheet conveying path;
• a detecting unit which detects each of a position of the side edge of a preceding sheet on the sheet conveying path and a position of the side edge of a succeeding sheet on the sheet conveying path at a location upstream of said punching member in the sheet conveying direction;
• a moving mechanism which moves said punching member in the sheet width direction;
• and
• a controlling portion which controls said moving mechanism so as to move said punching member based on the position of the side edge of the sheet detected by the detecting unit,
• wherein during a single job said controlling portion calculates a difference between the position of the side edge of the preceding sheet detected by said detecting unit and the position of the side edge of the succeeding sheet detected by said detecting unit, and said controlling portion controls said moving mechanism so as to move said punching member from a punching position at which the punching member punches the preceding sheet to a next punching position at which the punching member punches the succeeding sheet along the sheet width direction, on the basis of the calculated difference.