Post-processing apparatus and recording material processing apparatus used therewith

A post-processing apparatus for a booklet which is a bundle of half-folded sheets of recording material and of which a back portion protrudes, comprising:

• a restraining unit that restrains a periphery of the back portion of the booklet;
• a pressing unit that presses the back portion of the booklet restrained by restraining unit so that a curved back face of the back portion of the booklet is formed into a flat back face;
• an expanding amount judging unit that judges the expanding amount of the booklet in a thickness direction thereof before the pressing operation by the pressing unit;
• and
• a relief amount adjusting unit that, based on the judgment result of the expanding amount judging unit, adjusts a deformation amount of the back portion of the booklet in the thickness direction thereof caused by the pressing operation of the pressing unit, the relief amount adjusting unit being located between the restraining unit and the pressing unit.