PURPOSE: To prevent treatment liquid for especially immersion from being contaminated and deteriorated by introducing compressed temp. controlled gas into the liquid in a treatment tank from the lower part of the tank and allowing the liquid to temp. controlling with the gas.

CONSTITUTION: Constant amount of compressed gas fed through a constant flow rate valve 1 is heated with a heater 2. Then the heated compressed gas is introduced from the lower part of the treatment tank 4 and uniformly bubbled and thereby treatment liquid is heated. Simultaneously liquid temp. in the treat ment tank 4 is sensed with a measuring element 5 and output of the heater 2 is controlled with a temp. regulator 6. Heat exchange is performed between the heated compressed gas and treatment liquid and temp. control of the treat ment liquid is performed and the treatment liquid is efficiently reached to the preset temp. Further a cooler is used instead of the heater and temp. control of the treatment liquid can be performed by using the cooled compressed gas as a medium.