Post-processing apparatus and image forming system

A post-processing apparatus comprising:

• a side edge part removing portion that removes a side edge part from a sheet;
• a side edge part housing portion that houses the side edge part of the sheet removed by the side edge part removing portion and that is able to be pulled out from an apparatus body;
• a guide plate that is inclined in a direction intersecting with a moving direction of the side edge part and guides the side edge part removed by the side edge part removing portion along the moving direction of the side edge part to the side edge part housing portion;
• and
• a second guide plate that is arranged between the side edge part housing portion and the guide plate, and is able to be transformed into a first form having substantially mountain-shaped inclined surfaces in which both end portions of the second guide plate along the moving direction of the side edge part are lower than a center portion of the second guide plate, and a second form having substantially valley-shaped inclined surfaces in which both the end portions are higher than the center portion.