To provide a paper post-processing apparatus having a control means for more effectively performing the process of folding a specific cardboard, such as a cover sheet.

The paper post-processing apparatus has built therein a paper feed tray, a means for feeding paper on the tray, a means for conveying the paper conveyed from an image forming apparatus body and the paper fed, and a paper folding means for folding the conveyed paper into two or three and discharging it, with the operation of the paper feeding and conveying means and the paper folding means being effected by instructions from the image forming apparatus body. If a bundle of paper consisting of the paper fed from the tray and the paper discharged from the image forming apparatus body to the paper post-processing apparatus includes cardboards, specific cardboard settings are made to fold the paper using a control method different from that for a bundle of paper consisting only of paper of standard thickness.