The present invention provides an image forming apparatus and a post treatment apparatus. The stapling section stapling a sheet has an opening. The opening has a first open side facing a moving direction of a recording medium moved by the medium moving section and a second open side extending along the moving direction. A shutter is near the second open side in the stapling section. The shutter has a first end axially supported in a freely rotatable manner on an upstream side in the moving direction for arranging the sheet at the stapling position, and a second end portion that hangs down toward the downstream side in the moving direction. When the sheet is not in the stapling section, the second end of the shutter hangs down to block the second open side. When the sheet enters the stapling section through the opening section, the second end of the shutter is pushed up by the axially supported end as the support shaft. Therefore, the image forming apparatus is capable of effectively preventing foreign body from entering the post treatment apparatus.