To provide an indirect type evaporative cooling unit capable of surely cooling only the air without humidifying it.

This indirect cooling method is proposed, as a humidity is also increased in a conventional method of directly cooling the air. For example, the indirect type evaporative cooling unit has evaporating phenomenon of the water by the dried air in a wet channel and performs cooling. The air in a dry channel receives the cold, so that its temperature is lowered. As the air passing through the wet channel is the humidified and cooled air similarly as the conventional one, it is discharged to the outside of the unit. On the other hand, as the air passing through the dry channel is the cooled air, it is utilized. The air can be cooled to a dew point temperature without humidified by taking measures to repeat these phenomenon several times.