PURPOSE: To machine a curved surface with any radius of curvature economically using a general-purpose lathe and inexpensive tools on the market.

CONSTITUTION: A rotating shaft 2 is provided on a base 1 which is mounted on a tool post A, and a holder 3 is mounted detachably at the upper end of the shaft. When the rotating shaft 2 is rotated by operating a wheel 5a of a drive mechanism, the tool edge position of a throwaway tip 4 which is fitted to the holder 3 is moved on a circle with its center at the shaft 2. Here a cutting is made with a feed of tool edge movement on the circle. Thus a curved surface with a radius of curvature from the center of the shaft 2 to the tool edge of the tip can be machined using a general-purpose lathe and standard tools.