A sheet post-processing apparatus includes a taking-in portion configured to support sheets conveyed with their leading edges in a conveying direction directed downward in a standing position and release the support of the sheets, a folding portion configured to crease the sheets, which are supported by the taking-in portion, by pressing and release the creased sheets into the taking-in portion, a loading portion arranged under the taking-in portion to load the creased sheets conveyed from the taking-in portion, a stitching portion configured to stitch a sheet bundle loaded on the loading portion, and a controller configured to execute conveying of the sheets to the taking-in portion and creasing of the sheets supported on the taking-in portion by the folding portion during stitching the creased sheet bundle loaded on the loading portion by the stitching portion.