To surely prevent the forming of dew on a dew formation preventing face by installing a blower facing the dew formation preventing face of a glass, a mirror face, etc., and continuously excluding steam trying to be sucked to the dew formation preventing face through the use of the wind force.

The blower 2 setting a solar battery as a main source is installed by facing the dew formation preventing face 1 such as a glass face, etc., of a building in contact with outside air to blow by the operation of this blower 2 to allow the wind force 4 to forcedly exclude steam 5 sucked to the face 1 to prevent the formation of dew. A dew formation preventing method like this can be executed also for the mirror face part, etc., of a washbowl and dresser set in a bathroom and the wind force generated from a blowing fan is given to a part of the dew formation at the mirror face part by rotating the blowing fan similarly to improve the state of forming dew to remove dew formation.