To highly efficiently execute staple treatment even if a large sized sheet, by simple constitution.

This paper sheet post-treating device 200 includes the first end binding treating part 210 and the second end binding treating part 220 in a vertical direction, and is provided with the first conveying passage 231 for conveying a paper sheet from an image forming device 100 to the first end binding treating part 210, the second conveying passage 232 branched from the first conveying passage 231, to reach the second end binding treating part 220, and the third conveying passage 233 converging the paper sheets from the first end binding treating part 210 and the second conveying passage 220. The paper sheet is conveyed in the other end treating part, during the time when discharge treatment is carried out from the staple treatment in one of end treating parts, out of the two end treating parts, to enhance an efficiency for the staple treatment, in the paper sheet post-treating device 200.