An accumulating unit (22, 24) for accumulating in a sheet accumulating part an individual or signature form sheet carried from an upstream side, and comprising the sheet accumulating part; the sheet accumulating part comprising: a front positioning part that is provided on a front side in a carrying-in direction of the sheet carried into said sheet accumulating part and that positions a front edge in the carrying-in direction of the sheet; and a rear positioning part that is provided facing the front positioning part on a rear side in the carrying-in direction of said sheet and that positions a rear edge in the carrying-in direction of the sheet, the front positioning part being configured to, when the sheet has entered the sheet accumulating part and immediately before the front edge in the carrying-in direction of the sheet has contacted the front positioning part, move away from the rear positioning part such that a distance of the front positioning part from the rear positioning part is larger than a length of the sheet in the carrying-in direction of the sheet, and, after the front edge in the carrying-in direction of the sheet has contacted the front positioning part, move closer to the rear positioning part such that the distance of the front positioning part from the rear positioning part is substantially equal to the length of the sheet in the carrying-in direction of the sheet, characterised in that the sheet accumulating part further comprises a paper guide provided above an accumulating position between the front positioning part and the rear positioning part, and the paper guide includes an inclined portion that inclines downward toward the accumulating position and that is configured to guide the sheet that has entered the sheet accumulating part to the accumulating position by a lower surface of the inclined portion. a front positioning part that is provided on a front side in a carrying-in direction of the sheet carried into said sheet accumulating part and that positions a front edge in the carrying-in direction of the sheet; and a rear positioning part that is provided facing the front positioning part on a rear side in the carrying-in direction of said sheet and that positions a rear edge in the carrying-in direction of the sheet, the front positioning part being configured to, when the sheet has entered the sheet accumulating part and immediately before the front edge in the carrying-in direction of the sheet has contacted the front positioning part, move away from the rear positioning part such that a distance of the front positioning part from the rear positioning part is larger than a length of the sheet in the carrying-in direction of the sheet, and, after the front edge in the carrying-in direction of the sheet has contacted the front positioning part, move closer to the rear positioning part such that the distance of the front positioning part from the rear positioning part is substantially equal to the length of the sheet in the carrying-in direction of the sheet, characterised in that the sheet accumulating part further comprises a paper guide provided above an accumulating position between the front positioning part and the rear positioning part, and the paper guide includes an inclined portion that inclines downward toward the accumulating position and that is configured to guide the sheet that has entered the sheet accumulating part to the accumulating position by a lower surface of the inclined portion.