A sheet bending apparatus and a sheet postprocessing apparatus are provided for improved alignment of recording sheets during center-folding. A center-folding unit mounted in a sheet postprocessing apparatus performs a center-folding processing to a stack of recording sheets aligned on their sides and placed in a sheet holding member. Side aligning is performed near a central portion in a sheet conveyance direction of the sheet holding member. The center-folding unit includes: two upper end aligning members positioned upstream in the sheet conveyance direction on the sheet holding member and movable equally in opposite width directions of the sheet holding member; and a pair of lower side end aligning members positioned on downstream in the sheet conveyance direction on the sheet holding member and are movable equally in opposite width directions of the sheet holding member and independently from the upper end aligning members.