A first heat transfer medium circuit includes a first path and a second heat transfer medium circuit includes a second path are formed independently from each other by operating a first switching valve and a second switching valve in conjunction with each other to make each of multiple flow passages of a first flow passage group communicate with either the first path or the second path. The first and second heat transfer medium circuits in which the first path and the second path are connected to each other in series is formed by operating the first switching valve and the second switching valve in conjunction with each other to make each of the multiple flow passages of the first flow passage group communicate with both the first path and the second path.