Sheet processing apparatus and image forming system

A sheet processing apparatus comprising:

• a conveyance unit configured to convey a sheet in a sheet conveyance direction;
• a punch member configured to be rotatably supported and punch a hole at a predetermined position in the sheet being conveyed by the conveyance unit;
• a sensor configured to change an output value based on presence/absence of the sheet at a detection position positioned upstream of the punch member in the sheet conveyance direction;
• a driving source configured to rotatably drive the punch member;
• and
• a control unit configured to control the driving source,
• wherein the control unit is configured to
• (1) control the driving source based on a punching gap distance between a last punching position of a preceding sheet and a first punching position of a succeeding sheet in the sheet conveyance direction, and a rotational position of the punch member, and
• (2) perform an avoidance process of avoiding a punching process of punching the hole in the succeeding sheet in a case where the control unit judges not to perform the punching process in the succeeding sheet based on the punching gap distance and the rotational position of the punch member when the succeeding sheet has reached the detection position.