PURPOSE: To enable to prevent the performance deterioration of a condenser upon reverse washing by a method wherein baffle plates as well as air extracting tubes for the condenser are mounted near both tube plates and the air extracting tubes are used by switching them upon the reverse washing.

CONSTITUTION: Cooling water is flowed into cooling tubes 4 in a direction shown by an arrow sign 11a upon the ordinary operation of a condenser, therefore, a valve 10a is opened and a valve 10b is closed while the air extracted by utilizing baffle plates 7a as well as the air extracting tube 2a at the side of one of tube plates 8a. On the other hand, when the reverse washing operation of the condenser is effected, the flow of the cooling water is changed into the direction shown by the arrow sign 11b, therefore, the valve 10a is closed and the valve 10b is opened to extract the air by utilizing the baffle plate 7b as well as the air extracting tube 2b at the side of the tube plate 8b. According to this method, the performance deterioration of the condenser may be prevented upon the reverse washing.