Abstract: Provided is a new method of measuring involute gear tooth profile that differs from the base circle method and enables measurement of super-large gears without increasing the size of the tooth profile measuring machine and without increasing shift of the machine center of gravity. Measurement is performed during simultaneous ? axis control for rotating a test gear around the gear axis, X axis control for reciprocating a probe toward and away from the gear axis, and Y axis control for reciprocating the probe perpendicular to the X axis, thereby moving the probe along a line of action.