A sheet post-processing apparatus has a sheet conveying portion which receives and conveys a sheet discharged from an apparatus on an upstream side, and discharges it to an apparatus on a downstream side or a discharge tray, a sheet post-processing portion which carried out post-processing on the sheet, and a power saving control portion which renders the sheet post-processing apparatus into a power saving state, and the power saving control portion maintains electric power supply to the sheet conveying portion, and interrupts electric power supply to the sheet post-processing portion. The sheet post-processing apparatus, even in the power saving state, is capable of discharging the sheet discharged from the apparatus on the upstream side to the apparatus on the downstream side or a discharge tray.