To provide a heat exchanger and a sealed cooling tower capable of properly cooling the cooling water by a small amount of sprayed water without enlarging a plate fin, and being stably controlled regardless of air-conditioning load and the outside air temperature.

The plate fin 41 of this heat exchanger 11 receives the sprayed water to cool a circulated liquid refrigerant by heat exchange, and is provided with a plurality of linear ridge-shaped portions 43a, 43b not intersecting with each other, and a plurality of hollow cylindrical portions 42 which penetrate through a plate face and through which the circulated liquid refrigerant or its tubes are passed. Further the plate fin 41 is made of copper, and the linear ridge-shaped portions 43a not divided by the hollow cylindrical portions 42 and the divided ridge-shaped portions 43b divided by the hollow cylindrical portions 42 out of the plurality of ridge-shaped portions 43a, 43b are alternately arranged.