It removes radioactive sludge and corrosion products deposited on the inner walls of the pipes and valves in replacement or decommission, upon termination of life time, of nuclear power plant or nuclear facility. It lowers a cost of waste treatments taking advantage of a reduction of quantity of radioactive wastes by treating in classification of the radioactive wastes whose activities are lower than legal standards. The cleaning or decontamination methods developed until now have induced a damage on systems while being operated. A decontamination has been restrained if it was difficult to access physically. We are in development of the cleaning technique for pipelines by utilizing micro-bubbles in order to improve an efficiency and to prevent from any damage of systems. It aims to conduct a decontamination for spaces difficult to access there by applying cavitation phenomenon that is generated in collapse of micro-bubbles. In order to improve an efficiency of the micro-bubble device, the experimental conditions suitable to decontamination have been established and the auxiliary equipments have been added. The generation conditions and characteristics of micro-bubbles have been demonstrated by adjusting pHs and temperatures of cleaning solution. A decontamination effect has been confirmed by adding up an electrolytic method and ozone into micro-bubbles.