To surely prevent intrusion of flying insects, which obstruct business activity in a building for use as a store, and to eliminate increase in energy consumption for prevention of bad influence upon a human body and the environment.

In this cooler having an insect-proof function, the interior of the building is kept at positive pressure by blowing intake outside air cooled by evaporation of water, and flying insects are removed to the outside by blowing out the air to a window of the building and an entrance, whereby the flying insects can be prevented from entering the interior through a gap, the window and the entrance of the building, and the building is cooled.