To provide a cooling tower friendly to environment to prevent breading of microorganism, such as algae and Legionella, even when circulation water staguatls in a tower body for a long period of time and prevent an adverse influence from being exercised on the ecosystem of animals and vegetables even when circulation water is discharged from a circulation route.

Circulation water is sprinkled from the upper part of a tower body 1 incorporating a filler 2. Outside air sucked from the outside of the tower body is brought into gas liquid contact with circulation water flowing down along the surface of the filler 2 to effect cooling. A device 8 is provided to inject a solution containing metallic ion, such as silver and copper, in a cooling and circulation route at every given time.