PURPOSE: To make it possible to increase the heat transfer accelerating effect of the lower stage heat transfer pipe by a method wherein in the condenser provided with the group of multistage horizontal heat transfer pipes, the sectional area of the grooves formed on each of the heat transfer pipes in the flow direction of air, the sectional area of the space between the fins attached to the pipe or the sectional area of the space between the wires attached to the pipe, is increased the more the stage of the pipe group is lower.

CONSTITUTION: The pitch of the grooves 6 formed on the lower grooved heat transfer pipe 5 of the group of horizontal heat transfer pipes of the condenser 3 is made larger than that of the grooves formed on the upper heat transfer pipe to thereby increase the sectional area of the groove 6. Likewise, the sectional area of the space between the fins attached to the finned heat transfer pipe or the sectional area of the space between the wires attached to the wired heat transfer pipe is increased as the pipe is installed at the lower stage. With the above structure, even the grooves on the lower stage heat transfer pipe are not completely filled with a condensing liquid and the accelerating effect for heat transfer of the pipe is not lost. Accordingly, it is possible to make the body of the condenser compact and to reduce the manufacturing cost thereof.