PURPOSE: To grasp the distributing condition of indoor temperatures correctly with few sets of temperature measuring instrument.

CONSTITUTION: A room is constituted of first measuring divisions 6a-6c, which receive the affection of heat energy radiated from side wall surfaces 5a-5c in a room 2 respectively, and second measuring divisions 7, 8, which will never receive the affection of heat energy, while only 2 sets of temperature measuring instrument are arranged in the second measuring divisions 7, 8 and 10 sets of temperature measuring instrument are arranged in the first measuring divisions 6a-6c. According to this method, the installation of the temperature measuring instruments can be facilitated and the labor of a measuring person can be reduced. On the other hand, a facility necessary for the measuring works of distributing condition of indoor temperatures is miniaturized and charge for measurement can be reduced.