PURPOSE: To improve wide applicability by connecting a brine piping through a selector valve to a heat exchanger in an interior unit duct in such a manner that the brine piping may be selectively communicated with a higher and lower temperature source.

CONSTITUTION: When cooling a compartment, a first and second selector valve 66 and 69 are switched to form a closed circuit among brine pipes 61 and 62 and a lower temperature source pipe 67 with brine circulated by a pump 63. On the other hand, when heating the compartment, the selector valves 66 and 69 are switched for heating to form a closed circuit among the brine pipes 61 and 62, a bypass pipe 65 and a higher temperature source pipe 68 with the brine heated and circulated by an engine 4. With this constitution, the heat exchanger may be used for both cooling and heating, thereby improving wide applicability.