To provide a sheet post-processor and an image forming apparatus constituted so that a warning of the replacement time of a cutting member is given by detecting the load of the cutting member, and then, the deterioration of the cutting accuracy is prevented.

The sheet post-processor is constituted so that the sheets are pressed by a bundle pressing member 521 and the sheets are cut by a rotating blade 501, and also, provided with a cutter motor 521 for driving the rotating blade 501, an encoder disk 523 for detecting the load of the cutter motor 521 and a cutter clock sensor 522.