PURPOSE: To improve workability by a method wherein a fastening tool is mounted on a rotary shaft, and a clutch moved forward and backward by a switching means to rotationally drive a rotation drive source is positioned facing the rotary shaft and a holder for the fastening tool.

CONSTITUTION: By pressing a witch lever 5, a motor 3 is run by means of a microswitch 8, and a rotary shaft 12 is rotated. A clutch 13a for transmission is moved forward against the elasticity of a spring 14 along with rotation of a rotation member 9 and engaged with a clutch 13b of a holder 20, and rotational movement of the rotary shaft 12 is transmitted to the holder 20 and a jaw 22. A wire is twisted by means of a hook part 23 of the rotating jaw 22 and reinforcing bars are fastened.