PURPOSE: To provide a circulating hot bath machine which purifies water always properly irrespective of the size of a bathtub and the amount of water in the bathtub.

CONSTITUTION: A control circuit controls the amount of a purifying solution to be incorporated into bath water by a pump 8 on the basis of the bottom surface area of a bathtub set up by a bathtub bottom surface area setting key installed on a control panel and the water level of the bathtub measured by a level sensor 4.