To provide 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. A blind rivet fastening tool comprises a hollow nose housing (52) for housing a mandrel (20); a nose piece (51) provided at a front end of the nose housing (52), the nose piece (51) having an opening (59); a floating piece (60) provided at a front end of the inside of the nose piece (51); the floating piece (60) having a though hole (64) in which the mandrel (20) is inserted; a jaw guide (53) provided at the back side of floating piece (60), the jaw guide having an inside surface which has a smaller diameter toward the front end thereof; jaws (54) provided inside the jaw guide (53) for holding the mandrel (20); a pulling head (55) for pulling the jaw guide (53) in a back direction, and a jaw pusher (56) for pushing the jaws (54) in the forward direction.