PURPOSE: To always provide excellent heat exchanging function, by providing a distributing ratio regulating means which varies a ratio of a heating medium liquid feed quantity to a first heat transfer partition wall, partitioning a second flow passage for a first heating medium fluid from a first flow passage, to a heating medium liquid feed quantity to a second heat transfer partition wall, partitioning a third flow passage for second heating medium fluid from the first flow passage.

CONSTITUTION: From a first flow passage 14, through which high temperature or low temperature heating medium liquid flows down, a second flow passage 15 for first heating medium fluid is partitioned by means of a first heat transfer partition wall 16, and a third flow passage 17 for second heating medium fluid by a second heat transfer partition wall 18. A pair of distribution passages 19a and 19b, through which heating medium liquid is fed, are separately situated in a heating medium liquid feed passage 19 and to the upper parts of the first and second heat transfer partition walls 16 and 18, and flow rate regulating valves V5 and V6, being continuously or intermittently finely regulatable of a flow rate, are situated in the distribution passage 19a and 19b, respectively. A ratio Q1/Q2 of a heating medium liquid feed quantity Q1 to the first heat transfer partition wall 16 to a heating medium liquid quantity Q2 to the second heat transfer partition wall 18 is varied so as to cope with a fluctuation in cooling, heating, hot water feed and other loads on first and second heating medium fluid.