To conduct honing by removing clogging if clogging occurs at a sizing nozzle in a honing tool.

In an air circuit 19 where the sizing nozzle 13 of a honing tool 1 and an air source 17 are connected, a regulator 21 is mounted, and an A/E converter 23 which detects back pressure when air is jetted from the sizing nozzle 13 is connected. A selector valve 27 is provided at a bypath circuit 25 formed so as to directly-connect the air source 17 and the sizing nozzle 13. If clogging is detected in the sizing nozzle 13 by the A/E converter 23, the selector valve 27 is opened to introduce high pressure air of the air source 17 into the sizing nozzle 13 and blow off deposit adhering to the sizing nozzle 13 with high pressure air.