PURPOSE: To eliminate the heat resistance at the time of heat transfer, to reduce the heat loss, to improve the heat exchanging efficiency and to reduce the maintenance and management expenses by eliminating the indirect heat exchange of gas with liquid via a tube wall, fins, etc.

CONSTITUTION: Liquid 5 to become a heat receiver is poured in a heat insulated liquid tank 3, and gas having cold heat or warm heat is sent to the liquid 5 as bubble B. After the gas is brought into direct contact with the liquid 5, the gas discharged from the surface of the liquid 5 is recovered, thereby heat exchanging the gas with the liquid 5.