A first heat medium is circulated in a first circulating path (engine cooling circuit) of a heat source (engine) to cool the heat source down by the first heat medium, and exhaust heat from the heat source is absorbed by the first heat medium. A second heat medium is circulated in a second circulating path (exhaust heat recovering circuit) to exchange heat of exhaust air with the second heat medium, and heat of the first heat medium is exchanged with the second heat medium circulating in the second circulation path. The heat of the second medium to which heat is applied due to these heat exchanges is stored in heat storage means (heat storage tank).