A post-processing apparatus, including a stacker which stacks sheets, including a sheet stopping member which aligns the sheet and an urging member which urges the sheet to move toward the sheet stopping member, an accumulating section which is positioned upstream of the stacker in a sheet conveyance direction, a first sheet detection section which is positioned upstream of the accumulating section, and a control section which controls the accumulating section, based on a sheet detection signal, to superimpose a secondary sheet on a primary sheet in the accumulating section, wherein a leading section of the primary sheet is positioned toward an upstream side for a first predetermined length from a leading section of the secondary sheet, and controls the urging member to rub a leading section of the primary sheet which protrudes from the secondary sheet toward the sheet stopping member.