PURPOSE: To save a fixing work, the number of component parts and provide a positive protection by a covering pipe by a method wherein a flowing pipe and a passage for a reciprocating passage for coolant are integrally formed by the covering pipe.

CONSTITUTION: A connection pipe 1 has a parallel arrangement of two flowing pipes 11 of going pipe and a coming pipe for flowing coolant therein. A layer of foam resin 11b is formed outside the flowing pipe 11 and inside part and outside part are thermally insulated to each other. The layer 11b is connected at its central part and two flowing pipes 11 of going passage and coming passage in parallel to each other are integrally formed. An outside part of the layer 11b is formed with a flexible covering pipe 12 made of synthetic resin and a drain passage 13 is formed between the covering pipe 12 and a layer 11 of foam resin outside the flowing pipe 11. Use of such a connection pipe enables an indoor machine 2 and an outdoor machine 3 to be connected to each other without using any drain pipe. As for a draining, a knocking out part 13a adjacent to the drain passage 13 is provided from an end part of the connection pipe 1 or in the midway of the covering pipe 12 and then the drain is made at this part.