To facilitate the diffusion of PCB in a solid, to shorten a time required for decontamination and to improve the efficiency of cleaning when PCB is decontaminated from an impregnatable object to be cleaned by means of a solvent cleaning method.

When the decontamination of PCB impregnating contaminant is performed based on the cycle comprising the introduction of purifying cleaning liquid to a cleaning tank, the cleaning in the cleaning tank and the withdrawal of the cleaning liquid after cleaning from the cleaning tank, such a cycle that the cleaning liquid is once withdrawn after the cleaning, the temperature of the object to be cleaned is raised to a temperature of the boiling point of the cleaning liquid or more in the state of absence of the cleaning liquid, after keeping the temperature for a specified time, the cleaning liquid is again filled and the cleaning is performed at a temperature of the boiling temperature of the cleaning liquid or less is adopted.