An automatic screw gun which has a guide housing for the driving blade is equipped with a deflecting member that engages the leading end of the screw supply belt to deflect the leading end of the belt out of the path of the screw being driven, including the screw head or a washer below the screw head, whereby it is prevented that portions of the belt can be clamped between the surface of a work piece and the screw head or washer. A spring biases the deflector member into a rest position and the advancing belt brings the deflector member into a working position in which it holds the leading end of the belt out of the way.