According to one embodiment, a paper-sheet stacking apparatus includes a holding unit, a pushing mechanism, a backup, and a variable-force spring mechanism. The holding unit has a stacking base for holding a plurality of paper sheets in standing position and is configured to stack the paper sheets, one laid on another in a direction of a plane. The pushing mechanism is configured to push paper sheets transported, into the holding unit. The backup opposed to the pushing mechanism, is able to move in the direction the paper sheets are stacked and is configured to hold any paper sheet stacked between the backup and the pushing mechanism and to move away from the pushing mechanism as paper sheets are stacked one after another.