and a serrated irregular portion 105 d of the second ratchet 105 are not engaged causing no vibration whereby the impact drill is operated as the normal drill mode fig9 shows a weak stroke mode of the impact drill by turning the change lever 140 from the state of fig8 the steel ball 125 at the rear end of the spindle 102 is contacted with the face 141 c of the change shaft 141 having the smallest notch depth w 1 this notch depth w 1 is regulating the movement of the spindle 102 to the extent that the serrated irregular portion 104 a of the first ratchet 104 and the serrated irregular portion 105 d of the second ratchet 105 are lightly contacted at the tip in this positional relation even when the main frame portion 101 is pressed with a great force in the direction of the arrow the restoring force of the spring 120 is small and the impact force occurring between the first ratchet 104 and the second ratchet 105 is small accordingly when this small impact force is sustained this weak stroke mode is advantageous in prudently drilling the hard thin tile or the like fig1 shows a strong stroke mode of the impact drill by further turning the change lever 140 from the state of fig9 the steel ball 125 at the rear end of the spindle 102 is contacted with the face 141 b of the change shaft 141 having the larger notch depth w 2 this notch depth w 2 is regulating the movement of the spindle 102 to the extent that the serrated irregular portion 104 a of the first ratchet.