PURPOSE: To drill different diametrical circular holes by using a single tool.

CONSTITUTION: On a case main body 2, a central shaft 3 to be inserted into a hole previously formed in the center of a circular hole and a groove cutting cutter 4 to drill the circular hole on a plate body with revolution around the central shaft 3 as its center with a distance of radius length of the circular hole from the center of the central shaft 3 and in parallel with the central shaft 3 and by rotating by an electric motor M are provided, and simultaneously, a position changing means 5 varying distance from the groove cutting cutter 4 of the central shaft 3 is furnished.