To make set papers in a preparation completed condition ready to be stitched.

A sub-forming plate 10 is arranged to be vertically moved in a overlapped condition, on the sheetlike staple 2 supply side of a forming plate 4, and when the front end of the sheetlike staple 2 supplied by a feeding roller 11 when a power supply is switched on is not brought in contact with the sub-forming plate 10, the sub-forming plate 10 is retained in a position where the course of the sheetlike staple 2 is closed, and when the sheetlike staple 2 supplied by the feeding roller 11 is brought in contact with the sub- forming plate 10, this condition is detected and a detected signal is outputted. Further, the sub-forming plate 10 is vertically moved so that the sheetlike staple 2 is allowed to be sent just under the sub-forming plate 10 and the forming plate 4.