To detect air leaks in an air system of an air micrometer provided in a honing machine.

The method is for detecting the presence or absence of air leak in an air system by loading a honing tool 1 on a spindle of a honing machine to hold a sizing nozzle 13 provided in the honing tool 1 in a closed state, thereafter detecting the back pressure at the time when a specified air pressure is applied to the sizing nozzle 13, and comparing the detected back pressure to a set value. The device is provided with a closing member 33 capable of closing the sizing nozzle 13 of the honing tool 1 loaded on the spindle of the honing machine, a regulator 25 capable of adjusting the air pressure to be applied to the sizing nozzle 13, an A/E converter 21 for detecting the back pressure at the time when the sizing nozzle 13 is closed, and an operations unit 29 provided with a comparison part for comparing the back pressure detected by the A/E converter 21 with a set value.