PURPOSE: To increase cooling efficiency by a method wherein bent sections are formed on a tube and the tube is connected to an upper tank and a lower tank in the condenser of vapor of cooling medium for the motorcar engine.

CONSTITUTION: The condenser is constituted of the upper tank 7, the tube 8 and the lower tank while the upper tank 7 is provided with a hole 7a, similar to the shape of the section of the tube 8, at the bottom thereof and the end face 8a of the tube 8, which is formed into the shape of a flange, is abutted against the lower surface 7b of the hole 7a to connect them by a blazing or the like. The section of the vapor path of the tube 8 is formed so as to have sharp protuberances to elongate the peripheral length of the bent sections 8c, effecting the function of fins, reduce the flow path area F of the vapor ad increase the heat radiating area of the tube 8.