Hot water is sprayed to fillers arranged immediately under a hot water vessel through spray ports opened on a lower surface of the hot water vessel. The hot water flowing down along the fillers is cooled through direct contact with ambient air. The cooling tower comprises the fillers partitioned alternately into permanent wet and wet-dry changeover regions which are mutually isolated for flow passages of the ambient air and spray pipes provided on the lower surface of the hot water vessel exclusively for the wet-dry changeover regions such that the hot water can be sprayed to the wet-dry changeover regions separately from the permanent wet regions. The hot water vessel is supported by the spray pipes. The spray ports of the hot water vessel is communicated only with the permanent wet regions.
