A case is mounted to the outer portion of the bottom portion of the shank through a bearing and an absorption rod is situated in an axial hole provided in the axial direction on the bottom of the shank such that it is slidable in the axial direction. An absorption spring for urging the absorption rod in the axial direction is installed between the absorption rod and the shank and a tiltable case is situated on the bottom within the case such that it is capable of tilting with respect to the axial line. A holder is situated rotatably through a bearing within the tiltable case. A slidable holder provided with a chuck portion for a tool at a leading end thereof is situated slidably in the axial direction and the bottom end portion of the absorption rod and the top end portion of the holder are connected to each other through a universal joint. A tilt supporting pin unit in which a plurality of tilt supporting pins are directed downward and projected by being urged by a spring is situated within a case located around the outer peripheral portion of the universal joint and the tips of the tilt supporting pins of the tilt supporting pin unit are brought into contact with a pressure receiving plate provided above the tiltable case.
