A sheet buffer apparatus retains a sheet to be conveyed to a post-processing unit and is configured to perform post-processing for a sheet. The apparatus comprises a buffer unit configured to perform buffer processing to retain a sheet to be conveyed to the post-processing unit and overlay the sheet to be retained and a succeeding sheet, a determination unit configured to determine whether a sheet is inhibited from the buffer processing by the buffer unit, and a control unit configured, when the determination unit determines that the sheet succeeding the sheet to be retained is a sheet for which the buffer processing is inhibited, to control the buffer unit not to perform the retaining of the sheet to be retained.