PROBLEM TO BE SOLVED: To prevent the trouble of the storing water in a protective pipe which is not resulting from a rain water and a ground water. SOLUTION: By finding the fact that the moisture in the outer air is diffused and moved from the opening to the inside of a protective pipe 3, and condensed, so as to make the cause to generate a large amount of storing water, a means 5 to block the opening communicating from the buried protective pipe 3 and a buried box, to the outer air, is provided. The lid 9 of the manhole 8 of the buried box is made in a double structure, and one side lid 9a is preferable to make in a watertight and an airtight structure. Of a blocking means 5, at least one position is preferable to provide a check valve 5a or a liquid seal device which communicates from the protective pipe side to the outer air side, or a control valve to be opened and closed depending on the measuring value of the temperature or the pressure at the protective pipe side may be provided. The heat feeding is not stopped for a long period, or a large amount of cost is not used for the repairing.
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