PURPOSE: To improve the aligning accuracy, shorten the time required for alignment, and prevent the centering operation from becoming dangerous by providing a spindle for performing alignment of the center of rotation of a table with the position of a cutting tool positioned at the tip of a spindle head at the center position of the table.

CONSTITUTION: A small diameter spindle 2 is fixed to a table 3 through a hole part 3A provided in the center of the table 3 by means of a casing 2A, and a spindle motor 2B is provided at the lower end of the spindle. An upper end part 2C is positioned opposite to a cutting tool 6 positioned at the tip of a spindle head 5 fitted onto a cross-rail of a large vertical lath 1, is shaped into a disc, and has the same plane as the table 3. A test piece 7 is placed on the center position of the upper end part 2C of the small diameter spindle 2 to rotate only the spindle motor 2B instead of rotating the table 3. Then, the diameter of a vortex formed on the test piece 7 is measured to measure an error between the centers of the table and the tool 6. Thus, the position of the cutting edge of the tool 6 is changed depending on the center error to align the center of rotation of the table with the center of the tool.