Patent ID: 7520497

Claim:
A sheet processing apparatus comprising: a skew correcting portion which performs skew correction of a sheet while the sheet is being conveyed; a punch unit which performs punching of the sheet while the sheet is being conveyed; a punch driving portion which drives the punch unit at a trailing portion of the sheet; a sheet-edge detecting sensor which performs detection of a sheet edge in a direction intersecting with a sheet conveyance direction; a punch-unit moving device which moves the punch unit in the direction intersecting with the sheet conveyance direction; a sheet detecting sensor which performs detection of a sheet position in the sheet conveyance direction; and a controller portion which controls the skew correction of the sheet and a punching operation on the sheet, wherein: the punch unit is provided on an upstream side of the skew correcting portion in the sheet conveyance direction, the sheet detecting sensor is disposed in a position where a trailing edge of the sheet is detected after termination of the skew correction by the skew correcting portion, the controller portion controls such that after skew of the sheet is corrected by the skew correcting portion, positioning of the punch unit in the direction intersecting with the sheet conveyance direction is performed by the punch-unit moving device in accordance with a detection result of the sheet-edge detecting sensor, and punching is performed on the sheet by the punch driving portion in accordance with a detection result of the sheet detecting sensor, and when the sheet detecting sensor has detected the trailing edge of the sheet before termination of the skew correction by the skew correcting portion, the controller portion inhibits a punching operation by the punch unit.