To shield a lower water tank from light simply and surely by the arrangement of light shielding plates.

A plurality of the light shielding plates 12 having water resistance and light resistance are extended continuously around the whole peripheral surface of a louver 10 for an opposed flow type cooling tower A under a condition that an intake passage 11 for outdoor airflow is secured. Upon the operation of the cooling tower A, the outdoor airflow is sucked into the main body 13 of the cooling tower A from the intake passage 11 through the louver 10 and is contacted with cooling water in the state of opposed flow whereby the cooling water is cooled by the latent heat of vaporization accompanied by the evaporation of the cooling water and is collected into the lower water tank 20 of the cooling tower A, then, is supplied to a load unit or a refrigerating machine, for example. In this case, light beams from outside and especially the solar light is shielded by the light shielding plates 12 whereby the solar light will not pour on the lower water tank 20 of the cooling tower A and the generation of alga due to photosynthesis is eliminated thereby restraining the growth of bacteria or the like especially the growth of Legionella bacterium.