To perform reliable sterilization of the internal part of a treatment housing and to perform reliable washing and sterilization treatment after cooling processing of an article.

The internal part of a processing housing 21 is cooled by a cooling heat-exchanger 22 and articles are continuously inputted to the internal part of the processing housing 21 to effect cooling processing of the articles. During the cooling processing, outside air is precooled and dehumidified. After cooling, sterilization treatment is effected by an ultrahigh performance filter 34, the sterilized low temperature introduction air is introduced in the processing housing 21. Meanwhile, after cooling treatment of the articles, the internal part of the processing housing 21 is washed and treated and sterilization treatment is effected. Thereafter, drying and processing of the processing housing 21 are effected and simultaneously, hot and humid internal air in the processing housing 21 is discharged to an external part, and the internal part of the processing housing 21 is maintained in a sterilized state.