PURPOSE: To increase the condensing performance in a main condenser and prevent overcooling of condensed water by a method wherein a pre-condenser is provided at the upstream side of the group of heat transfer tubes of the condenser for a steam turbine or the like and condensed water, generated in the pre- condenser, is discharged directly by a drain catcher.

CONSTITUTION: A pre-condenser 20 is provided at the upper upstream side of a condenser section 11 to pre-condense the steam (b) flowed into a steam inflow section 12. The group of drain catchers 21 is provided at the lower side of the group 20a of cooling tubes of the pre-condenser 20 remaining steam flowing intervals 21c and produced condensed water arrives at a drain reservoir 13, provided below the drain catchers, along the inner wall of a case from both ends of the case. The generating amount of condensed water in the condenser section 11 is comparatively small by the provision of the pre-condenser 20 and the condensed water in the pre-condenser 20 is not provided to the condenser section 11, therefore, water film is not produced on the cooling tubes 11a of the condenser 11, the heat conductivity of the tubes is increased and general steam condensing performance may be improved.