Pivotal post processing tray

An image forming apparatus comprising:

• an image forming apparatus main body having an upper portion, and a sheet electing section with a sheet ejection port,
• a placing tray formed on the upper portion of the image forming apparatus main body and located under the sheet ejection portion to receive a sheet ejected from the image forming apparatus main body thereon,
• an image reading device for reading an image disposed above the sheet ejecting section to cover the placing tray, and
• a sheet post-processing unit disposed between the image reading device and the placing tray and detachably attached with respect to the sheet ejection port, said sheet post-processing unit including supporting means capable of moving between a support position for supporting an upstream side of a sheet ejected in a transfer direction and a retreat position for allowing the sheet to drop onto the placing tray located immediately under the supporting position, post-processing means disposed at a side adjacent to the supporting means for applying post-processing to the sheet supported on the supporting means, sheet shift means for moving the sheet into the post-processing means and setting the sheet therein, and means for transferring the sheet shift means.