PURPOSE: To select high-speed rotation for a tool of small diameter or low-speed rotation for a facing tool.

CONSTITUTION: When hole machining such as drilling is done by using a third spindle 40, a central axial line of a second spindle 51 agrees with an axis of a third spindle 40. After this, a cylinder 48 is driven to operate a shifter 45 in order to make teeth of a shift gear 43 mesh with an internal tooth gear 50. A motor is actuated, a pulley is rotated, and the third spindle 40 is rotated at high speed to drive and rotate the internal tooth gear 50 and the second spindle 51. A tool Ta of small diameter is rotated in a housing 10 due to this drive.