PURPOSE: To enable to perform a cooling work effectively by a method wherein a flexible film, which will be contacted to a circuit substrate, comes in contact with the flow of a liquid refrigerant, and the circuit substrate is cooled by the liquid refrigerant through the flexible film only.

CONSTITUTION: A window 21, to be corresponding to the circuit substrate 5 of a circuit devices, is provided on the main surface plate 19 of a container 20 for refrigerant circulation. On the other hand, a thermal conductive and flexible film 22, which was formed by closing a window 21 on the main surface plate 19, is protruded on the side of a substrate 5 of the device 7 by the pressure of the liquid refrigerant 9 circulating in the container 20 through the window 21, and the film 22 is provided in such a manner that it comes in contact with the substrate 5. As a result, the flexible film 22 comes in contact with the circuit substrate 5 securely, and an efficient cooling can be accomplished.