We obtained the following data of a structure generating cold air drainage flow. 1) A remarkable cold air drainage flow was observed all through the night in the area. 2) Wind velocity was less than 1.0m/s but the air temperature was apparently lower than the outskirts of the area. 3) The heat collectible area largely affects the strength of cold air drainage flow (temperature drop and wind velocity). 4) Role of vegetation cold heat source depends on the lay of the land in the upper area on a slope and the use of land. 5) Crowned vegetation may generate more cold air.