PURPOSE: To avoid an increase in optimum tightening torque while absorbing machining torque of a chip by maintaining the optimum tightening torque invariably while guaranteeing the disassembly of a hollow cone and a carrier in a joint for tool holding device of a machine tool.

CONSTITUTION: A shaft 9 fits a carrier 6 and is guided into a seat in the axial direction 2 of a mounting cone 1 while a ball 17 is stored in a groove 16. A tightening spanner guided through a hole 14 of the cone 1 is engaged with a recessed part 13 of the shaft 9 and is rotated so as to thread and fix a screw end 11. A screw stop of the shaft 9 moves a shank 7 within an inner cylinder guide 4 of the seat 2 in cooperation with a crown of the ball 17. The seat 2 puts a tongue piece 22 into a recessed part 20 so as to prevent the rotation of the carrier 6. Tightening is continued until tightening reaches the optimum torque generated due to the friction between faces 5 and 21. During tool machining, machining torque in an end part of a tool is absorbed by the tightening torque, and high torque during chip cutting is absorbed by the tongue piece 22.