According to one embodiment, a sheet post-processing apparatus includes a standby unit, a processing unit, and a discharge unit. The standby unit puts a sheet on standby. The processing unit is disposed below the standby unit. The processing unit includes a conveyance reference plane, a distance between which and a conveyance reference plane for the sheet in the standby unit changes to decrease from an upstream side toward a downstream side in a conveying direction of the sheet. The processing unit processes the sheet supplied from the standby unit. The discharge unit is disposed on the downstream side in the conveying direction of each of the standby unit and the processing unit. The discharge unit is provided with an opening section for causing the sheet discharged from the standby unit or the processing unit to pass.