To desirably secure internal diameter measuring accuracy relating to a processing hole, by adjusting a characteristic of an air micrometer changed by a delicate shape difference of an air nozzle and an action environmental change.

A master ring 27 having a reference hole 25 relating to a processing hole H is formed in a shape gradually changing an internal diameter along a circumferential direction so as to be in the same shape to the machining hole H, air is blown relating to an internal surface of the machining hole H, based on this back pressure, a machining hole internal diameter is measured by an air nozzle 15, a honing head 1 having the air nozzle 15 is inserted into the master ring 17, in a rotated condition, air is blown to an internal peripheral surface of the master ring 27 from the air nozzle 15, here an internal diameter change is obtained along a circumferential direction, a measured value according to the internal diameter change is used to serve as a proper dynamic characteristic of this air micrometer. In the case of this dynamic characteristics data being out of a specified range, a hole diameter of the air nozzle 15 is adjusted to put it into the specified range and honing work is performed by the adjusted air nozzle 15, while measuring an internal diameter of the processed hole H.