First circulation portions switch a flow of a heat transfer medium such that one of the heat transfer media for two systems selectively circulates through a radiator flow path or a first bypass flow path. Second circulation portions switch the flow of the heat transfer medium such that the heat transfer media for the two systems selectively circulate with respect to a second flow path group. The first circulation portions and the second circulation portions are adapted to switch the flow of the heat transfer medium so as to form a first circulation circuit for allowing the heat transfer medium to circulate among a first flow path group, the second flow path group, and a first pump, as well as a second circulation circuit for allowing the heat transfer medium to circulate among the first flow path group, the second flow path group, and a second pump.