The present invention is equipped with dissimilar metal connecting pipes (40, 41) for which an aluminum first pipe member (42) and a copper second pipe member (43) are joined together, and a cover member (48) that covers the surrounding area of the dissimilar metal connecting pipes (40, 41). The construction is such that a tubular sacrificial corrosion-preventing layer (46) having a corrosion prevention effect is provided on the outer circumferential surface of the first pipe member (42), and at the region of the outer circumferential surface of the first pipe member (42) that is covered by the cover member (48), a tubular non-corrosion-preventing part (47) is formed where the outer circumferential surface of the first pipe member is exposed due to the absence of the sacrificial corrosion-preventing layer (46), thereby bringing the non-corrosion-preventing part (47) and the cover member (48) into contact.