To give no perfunctory restriction to a joint flange part which is important to secure strength as a pressure container, by providing a temperature fuse on the bottom part of a heat exchanger unit.

A wall 8 is provided all around a temperature fuse 7 positioned at the bottom surface of a heat exchanger unit. A connecting part 10 of the temperature fuse 7 to a lead wire 9 is disposed at a lower part than a detecting part 7-a of the temperature fuse 7. The temperature fuse 7 with all sides surrounded by the wall 8 is sealed by a resin sealing material 11. A fixing part of the temperature fuse 7 is placed inside a flange 12 connecting the upper and lower heat exchanger unit if viewing by a projected area. Since the wall 8 is provided around the temperature fuse, even if the temperature fuse 7 exists on the bottom part of the heat exchanger unit and condensed water gathers around the temperature fuse 7 part, the temperature fuse 7 is insulated from the water, and there is no fear of causing corrosion in the detecting part of the temperature fuse 7.