To provide a sheet post-processing device capable of preventing scattering of needle tip dust coming from a stapler in a machine and achieving stable paper binding work.

This sheet post-processing device has a stack means for loading a plurality of sheets forming image on them, an aligning means for aligning a plurality of loaded sheets, a binding means having functions for binding a plurality of aligned sheets by a staple needle and cutting a needle tip of the staple needle and being movable in the direction of main scanning, and a needle dust storing means for storing cut needle tip dust. This sheet post-processing device is provided with a sensor for detecting height of deposit of needle tip dust discharged from the binding means moved to a predetermined position.