Sheet bundle folding apparatus with movable push-in member

A sheet bundle folding apparatus comprising:

• fixed folding member positionally fixed at a predetermined position;
• a movable folding member separably contactable with said fixed folding member;
• and
• a sheet bundle push-in member movable toward an area between said fixed folding member and said movable folding member to push a bundle of sheet into the area between said fixed folding member and said movable folding member;
• wherein said sheet bundle push-in member is capable of moving in a sheet folding direction along a guide groove via a sliding member,
• wherein said sheet bundle push-in member is capable of moving also in a retracting direction of said movable folding member by providing an allowance between said sliding member and said guide groove,
• wherein said sheet bundle push-in member follows a folding position of the bundle of sheet pushed into an area between said fixed folding member and said movable folding member by said sheet bundle push-in member, and
• wherein said sliding member includes two members provided along the sheet folding direction, and wherein one member of said two members has a width smaller than a width of said guide groove and the other member has a width substantially equal to the width of said guide groove.