To easily and securely clean the inside of a blind hole formed at a thin rod.

An intermediate stock 1 at which the blind hole 2 is formed is stored in a closed container 10. The pressure at the inside of the closed container 10 is reduced by a pressure reduction pump 11. Further, a cleaning liquid is fed from a liquid tank 12 so that the intermediate stock 1 and the blind hole 2 are immersed therein. The pressure at the inside of the closed container 10 is increased by a pressure increasing member 13. The cleaning liquid is discharged, and thereafter, the pressure at the inside of the closed member 10 is reduced once more, thus the blind hole 2 formed at the intermediate stock 1 is cleaned.