To provide a cooling tower structure for facilitating maintenance such as cleaning or repair by directly cooling oil to be a problem upon mixing with water.

Oil 23 of the side to be cooled is fed in a body 24, the air 25 of the side to be cooled is fed into an inner tube 32A of a tube 32 of a double tube structure having the tube 32A and an outer tube 23B, and an inner surface of the tube 32A is moistened with water 29. Accordingly, an outer surface of the tube 32B is not contaminated, but the inner surface of the tube 32A is contaminated. Dirt of the inner surface of the tube 32A is physically cleaned to insert and rub a cleaner such as a brush from one end of the tube 32 into the tube 32 even of a tube group 34 is provided in the body 24. Since the tube 32 has the double tube structure, oil to be a problem upon mixing with water like the oil 23 for a transformer can be directly cooled by a cooling tower 20.