PURPOSE: To remove foreign materials from the inside of a valve box by connecting one edge of a feeding pipe with an exhaust port and connecting the other edge in demountable manner with the feeding port of a compressed air feeding source and feeding the compressed air from the compressed air feeding source.

CONSTITUTION: In the state that a selector valve 13 is switched to the first passage, one edge of a feeding pipe is connected to an exhaust port 10a, and the other edge is connected in demountable manner with the feeding port 23 of a compressed air feeding source 20, and the fluid (sewage water) and foreign materials in a valve box 2 are pushed out into a drain pipe 1 by a compressed air stream by feeding the compressed air from the compressed air feeding source 20, and the foreign materials are removed from the inside of the valve box. Further, after the foreign materials are removed, the selector valve 13 is switched to the second passage, and a cleaning liquid recirculation pipe 37 is connected with the output of the second passage, and further, the other edge of the feeding pipe is demounted from the feeding port of the compressed air feeding source 20, and connected in demountable manner with the feeding port 34 of a clean liquid feeding source 30, and cleaning liquid is supplied from the cleaning liquid feeding source, and allowed to circulate, and the foreign materials are removed from the valve box 2.