To provide a paper conveying device, a paper post-processing device, and an image forming device enabling a reduction in size and manufacturing cost.

This paper conveying device C conveys paper after folding with the folded section of a folded paper bundle positioned at the head. The paper conveying device comprises a cutter unit 31 for cutting off the rear end of the folded paper bundle, an additional folding part 54 positioned on the downstream side of the cutter unit 31 and additionally folding the folded section of the paper bundle by moving along the folded section of the paper bundle, bundle conveying rollers 9a, 9b for conveying the paper bundle toward the additional folding part 54, and a single drive mechanism 35 for driving the additional folding part 54 and the bundle conveying rollers 9a, 9b.