To solve problems of a heat pump that necessarily has a large compressor for achieving high cooling efficiency, and that, with a circular piping constitution, has difficulty in discharging dissolved gas in water.

On a passage 10 for air in this heat pump 1, an air intake port 11, an expander 12, a vaporization container 13, a compressor 14, and an air discharge port 15 are provided in order. The air intake port 11 and the air discharge port 15 are opened to atmospheric air. Air taken from the air intake port 11 is adiabatically expanded by the expander 12 to be introduced into the vaporization container 13 where it becomes bubbles. Water is vaporized into the bubbles to be cooled. When air is adiabatically expanded, generated work is transmitted through a transmission mechanism 16 to the compressor 14 to be driving force.