Sheet processing apparatus that aligns sheets and image forming system

An image forming apparatus including:

• a sheet processing apparatus, and
• an image forming apparatus that is connected to the sheet processing apparatus, and discharges a sheet having an image formed thereon into the sheet processing apparatus,
• wherein the sheet processing apparatus comprises:
• a first alignment member and a second alignment member, each movable in a sheet width direction orthogonal to a sheet conveying direction, for aligning a sheet;
• a moving unit configured to move each of said first alignment member and said second alignment member in the sheet width direction;
• a detection unit configured to detect a skew amount and a skew direction of the sheet;
• and
• a control unit configured to control said moving unit to position said first alignment member and said second alignment member at respective predetermined standby positions before the sheet is received between said first alignment member and said second alignment member, and move one of said first alignment member and said second alignment member in a direction toward the sheet during conveyance of the sheet between said first alignment member and said second alignment member, based on the skew amount and skew direction detected by said detection unit.