PURPOSE: To provide a cooling tower and the operating method thereof, which are capable of preventing the generation of white smoke effectively while preventing the overcooling of a refrigerating machine.

CONSTITUTION: A hot-water bypassing route 21, introducing the hot-water of a hot-water pipeline into a cold water pipeline 15 to increase the temperature of cold water when the temperature of the cold water of the cold water pipeline 15 is lowered than a predetermined temperature, and a cold water bypassing route 22, introducing the cold water of the cold water pipeline 15 into the hot-water pipeline to lower the temperature of hot-water when a relative humidity is elevated than a predetermined relative humidity, are provided between the inlet channel of cooling water for a cooling tower or the hot-water pipeline and the outlet channel of the cooling water for the same tower or the cold water pipeline 15.