To provide a heat engine with high heat efficiency capable of doubling the heat efficiency by materializing the low isothermal compression of air and regenerating, as a recyclable heat resource, the heat energy of low quality, which was low temperature waste heat, by reducing an operating temperature.

The properties of air such that are compressible and low in density are combined with those of water such that are non-compressible and high in density to provide the synergic effect of the air and water abundantly present on the ground and sea level. The air in bubbled state is mixed with the water, and the water is pressurized and the air is compressed utilizing the centrifugal force of a centrifugal pump. At the same time, the low isothermal compression by air-water mixing and compression is materialized by making the compression heat of the air to be absorbed in the water, and the air and water are separated in a high-pressure space to provide a low-temperature, high-pressure air and a high-pressure water and to discharge the compression heat by injecting the high-pressure water and recover a pump drive power.