PURPOSE: To decide whether switching for cooling/heating should be done or not appropriately by making it possible to know the temperature of a room after switching, before the switching is done by a method wherein a reasoning unit which reasons the temperature in a building after switching is provided on the central process unit and at least one of function distributed terminals.

CONSTITUTION: Reasoning units 4 are respectively provided on a central process unit 3, which is connected with a CRT 1 and a printer 2, and a plurality of function distributed terminals 5. An input/output unit 6 is connected with the function distributed terminal 5, and outside temperature information, temperature information for cooling/ heating water which flows in an air conditioner 7, valve opening degree information to adjust the cooling/heating water quantity, and indoor temperature information in a living room 8 are input. When respective information is input in the input/output unit 6, the function distributed terminals 5 and the central process unit 3 fetch the information, and the reasoning units 4 reason how the temperature in the living room 8 changes at the time of switching for cooling/heating, and the reasoning result is output on the CRT 1 and printer 2. When the reasoning result matches a cooling set value or heating set value, switching is done, and when it does not match, the switching is not done.