To improve productivity by enabling a binding process and a folding process to be performed parallel.

The paper processing device includes a stapler 41 for binding a bundle of sheets of paper, a folding blade 55 for folding the bound bundle of sheets of paper in the middle, conveying rollers 56 and press folding parts 57. The paper processing device further includes: a gripping mechanism 44 including a reference plate 45aa for aligning the direction in which a bundle of sheets of paper are conveyed, and gripping parts 45a and 45b for gripping the bundle of sheets of paper; clamp vertical shafts 47 and 48 and a lifting/lowering guide 51 for lowering the gripping mechanism 44 from a paper gripping position L1 to a predetermined position L2 on the side of the a middle-fold unit 120 and lifting it from the predetermined position L2 to the paper gripping position L1; and first and second conveyance roller pairs 81 and 82 for receiving the bundle of sheets of paper from the gripping mechanism 44 moved to the predetermined position L2 and convey the bundle to the position of the folding blade 55 of the middle-fold unit 120. The paper processing device releases the bundle of sheets of paper from its gripped state at the predetermined position L2, thereby causing it to fall, and allows the lifting movement of the gripping mechanism 44 to the gripping position L1 while causing a folding process to be performed.