To carry out the measuring of a knife edge center position in the Y-axial direction of a rotary tool in a simple operation, by providing a touch sensor having contacts in the +Y axial direction and the -Y axial direction.

A worker moves an end mill T2 relatively in the manual mode, it is abutted to a contact 12b in the +Y axial direction side, and he reads the machine coordinates value Y2 of a machine coordinates system at the contacting time, from a moving shaft controller. Then, the worker makes the end mill T2 abutted to a contact 12a in the -Y axial direction in the manual mode, and reads the coordinates value Y1 in the -Y axial direction side from the moving shaft controller. The rotation center position error found from the coordinates values Y1 and Y2 and set data Y01 and Y02, and the diameter are stored in a memory area of a tool offset memory, corresponding to the correcting number of the end mill T2.