To provide a sheet post-processing device capable of post-processing a staple or the like in a stable behavior state of a sheet bundle, and an image forming device having it.

The sheet post-processing device and the image forming device typically comprise a conveying means for conveying a sheet to an aligning tray, an aligning means for aligning the side edge of the sheet bundle loaded on the aligning tray, a pressing member for pressing the upper surface of the sheet bundle aligned by the aligning means, and a post-processing means for applying a predetermined post-processing to the aligned sheet bundle. In the sheet post-processing device for performing aligning with the aligning means and pressing with the pressing member every conveyed sheet, the aligning is performed, pressing is not performed, and the post-processing is performed in the last page of the sheet bundle.