PURPOSE: To make only the screw fitted to a bit normally capable of thread fastening, by providing a detection means which detects as to whether or not the signal of a signal generation means is passed through the screw lower end peripheral edge held on a bit and a deciding means which decides the holding state of a screw according to the reception state of the detection means.
CONSTITUTION: At the time when the screw groove of the screw 1 head is correctly fitted to the screw thread of the bit 2 tip, the signal output from a signal generation means 3 is received by a detection means 4 by passing through the screw lower end circumference. At the time when the fitting state of the screw groove of the screw 1 head and the screw thread of the bit 2 tip is not enough and not fitted correctly, a gap is caused between the screw groove and thread thereof and the position of the screw 1 lower end is slipped, so the signal transmitted from the signal generation means 3 is checked by the screw 1 lower end and not received at the detection means 4. Consequently, a deciding means 5 detects the presence of the reception of the detection means 4, deciding as to whether or not the screw 1 is correctly held with its suction to the bit 2.
KOMORIYA HITOSHI
NOGO HIDETOSHI
YAMAMOTO YASUKI
