Patent ID: 8590881

Claim:
A sheet post-processing device comprising: a temporary holding unit temporarily holding a sheet supplied by an image forming apparatus; and a shifting unit performing a shifting operation on a sheet bundle, the sheet bundle including two or more sheets, wherein at least one extra sheet supplied by the image forming apparatus is not included in a sheet bundle; when one extra sheet is supplied by the image forming apparatus and when the shifting operation is not yet commenced on a sheet in queue immediately before the extra sheet when the extra sheet is received, the extra sheet is supplied to the shifting unit without holding the extra sheet in the temporary holding unit, the shifting operation is suspended until the extra sheet reaches the shifting unit, and the shifting operation is performed on the sheet in queue immediately before the extra sheet and on the extra sheet when the extra sheet reaches the shifting unit; and when one extra sheet is supplied by the image forming apparatus and when the shifting operation has commenced on a sheet in queue immediately before the extra sheet when the extra sheet is received, the extra sheet undergoes the shifting operation after the shifting operation on the sheet in queue immediately before the extra sheet has been completed.