PURPOSE: To easily inject a constant amt. of a chemical with no need for electricity and a battery by utilizing the circulating water flowing down from a cooling tower by the start of operation to integrate the operating time, and automatically injecting a constant amt. of the chemical.

CONSTITUTION: When the operation of the cooling tower 1 is started, circulating water flows down and enters a pan 4. The water is gradually collected in a cylinder 3 through a hole 6 of the pan 4, a valve 15 is opened when the balance with a weight 9 is lost, and air is taken into a chemical tank 14 through an air intake tube 12. As a result, the chemical is injected from the chemical tank 14 into the water reservoir at the bottom of the cooling tower 1 through a chemical tube 13. Since the water in the cylinder 3 flows down little by little from a thin tube 7, an integrated state as shown in the figure is obtained when the balance with the weight 9 is inversely lost, and the chemical is continuously injected until the valve 15 is closed.