PURPOSE: To shorten cutting time by so constituting the captioned device as to be able to accurately cut a curved face only by the axial directional travelling operation of a horizontal boring machine in cutting of the curved face with a large radius by the use of boring arbor of a general purpose horizontal boring machine.

CONSTITUTION: A tool holder 25 is set in such a way that the distance from the rotary center of the tool holder to the end of a cutting tool 32 becomes equal to the radius R of the curved face to be cut. And when a boring arbor 1 is rotated with rotation of the hollow shaft 2 of a horizontal boring machine, tool rest bodies 14a and 14b, a tool rest support 15, a tool rest base and gear box 20, and the tool holder 25 are rotated to cut the internal periphery of a workpiece or casing 3. Along with this, the shaft 6 with rack directly coupled with a main spindle 5 is continuously moved to rotate the pinion shaft 10 meshed to the rack 7. Rotation of the shaft 10 rotates the tool holder 25 through a worm shaft and a worm wheel. Therefore, the cutting edge of the cutting tool 32 can cut the R section provided in a hole with a large diameter by means of being mechanically fed.