A blind rivet fastening tool in which the jaws are open at the original position, and at a return step in which the tool is returned to the original position after a blind rivet is fastened the fastened blind rivet is pushed out. The tool comprises a hollow nose housing for housing a mandrel; a nose piece provided at a front end of the nose housing and having an opening; a floating piece provided at a front end of the inside of the nose piece; the floating piece having a though hole in which the mandrel is inserted; a jaw guide provided at the back side of floating piece and having an inside surface which has a smaller diameter toward the front end thereof; jaws provided inside the jaw guide for holding the mandrel; a pulling head and a jaw pusher for respectively pulling back and pushing forward the jaws.