PURPOSE: To perform easy and rapid replacement of a tool by means of a tool fixing precision machine utilizing surface jointing by engaging a main spindle end part with a tool base part as a wedge is pressed, specifying a relative position therebetween through rotation of a lock pin, and releasing pressure exerted on the wedge to effect fastening.

CONSTITUTION: A wedge 49 is pressed by means of a hydraulic cylinder 59 to release it downward, a lock pin 37 is rotated through press of a rack 39a by means of a hydraulic cylinder 57, and a flat surface 37a of the pin 37 is positioned flush with the side of a guide protrusion part 32. In which case, the tip of a protruding lever 78 is protruded in a lock groove 77 of the back of the rack 39a, and the proper position of the rack 39a is held to prevent rotation of the pin 37. A adapter 31 is lowered from above toward a tool attaching part 5, a V-protrusion 41 is inserted in a dovetail groove 33 to intercouple the two members. Thereafter, when pressure to the wedge 49 by means of the cylinder 59 is rendered ineffective, a protrusion lever 47 is protruded through the energizing force of a spring 48 and since the wedge 49 is pushed up, the mounting part 5 and an adapter 31 are strongly intercoupled. As noted above, the adapter 31 to which a tool C is fixed is attached to the mounting part 5, and through rotation of a main spindle 1, a cutting work is carried out.