To precisely and accurately provide the means of enabling control of a liquid surface inside a tank.

An electronic controller unit 11 controls the starting and stoppage of a pump 3 by the data supplied from a liquid surface sensor 12, where the electronic controller unit 11 is provided with a tank 1 of a high-temperature fluid generator provided with a heater 13 and the pump 3 feeding a low- temperature fluid into the tank 1, a liquid surface sensor 12 inside the tank 1 is provided with a float connected airtightly to the opening piercing with a flexible tube via a part of the tank 1 and an angle detecting switch detecting the change of the position of the float, and the flexible tube and the float of the liquid surface sensor 12 are positioned horizontally inside the tank 1.