PURPOSE: To efficiently clean the inside and outside surfaces of the small parts of a control rod drive mechanism to which radioactive clads are stuck by injecting a cleaning liquid to the inside and outside surfaces of the rotating parts to be cleaned, thereby automatically and continuously cleaning said parts.

CONSTITUTION: The cylindrical small parts of the CRD to which the radioactive clads are stuck are loaded on respective parts receiving bases of a cleaning tank 11. A motor is then driven to simultaneously rotate the parts receiving bases, then a circulation pump 53 and a high-pressure feed water pump 42 are driven to start cleaning of the parts. The cleaning water is regulated to a prescribed flow rate by a regulating valve 45 on the down stream of the pump 42 and is then regulated in flow rate by respective regulating valves 46, 47, 48 of branch pipes 41aW41c. This cleaning liquid is supplied to a nozzle 31 for cleaning the outside surfaces of the parts, a nozzle 32 for cleaning the inside surface of the parts and a nozzle 33 for cleaning the inside of the tank. The liquid is injected in the form of the high-pressure cleaning water of the prescribed flow rate from the respective nozzles into the cleaning tank 11. The small parts of the CRD which are loaded on the parts receiving bases and to which the radioactive clads are stuck are thus simultaneously cleaned in the total number from the inside and outside surfaces thereof.