A post-processing device (200) includes a circulation conveyance path, a zeroth conveyer (R0), and a controller (50). The circulation conveyance path includes a first conveyance path (W1), a second conveyance path (W2), a third conveyance path (W3), a first conveyer (R1), a second conveyer (R2), and a third conveyer (R3). The first and second conveyers convey a preceding sheet (P1) along the first and second conveyance paths. The third conveyer conveys it from the third conveyance path to the first conveyance path. The zeroth conveyer conveys a following sheet (P2) toward the first conveyer. The controller controls the third conveyer to stop the preceding sheet, subsequently controls the zeroth conveyer and the third conveyer to overlay the preceding sheet with the following sheet to form a sheet bundle (Q) having a shift amount (G) between a leading edges of the preceding sheet and the following sheet and strike the leading edges of the preceding sheet and the following sheet against the first conveyer.