PURPOSE: To provide a circulator for circulating a stored liquid in a tank into a desired channel wherein when the liquid level in the tank is lowered, a float can seal an upper opening of the tank so that the liquid leakage can be prevented and operations such as pumping for circulation is made to be stopped.

CONSTITUTION: In the operation of the device, when the circulator is used for circulating hot water through a panel (a) for floor heating, water is introduced through a water introducing cylinder 33 of the circulator 1 to fill the panel (a) and a pipe 2 and further to fill to an upper part of a vent cylinder 31 through a heator tank 3. In this state, the float 81 will be floated to make a lead switch 83 ON. Then, when a main switch 5 is switched ON, a heater 9 generates heat and a pump (not shown) in the circulator 1 is operated to circulate the heated water. If there is any liquid leakage somewhere in the circuit during its circulation, the water level in the vent cylinder 31 will be lowered to switch OFF the lead switch 83, and therefore the operations of the heater 9 and the pump 4 will be stopped and a closing lid 11 will close a communication hole 12 tightly.