PURPOSE: To improve a follow-up characteristic into a set temperature by a method wherein an operation target temperature is optionally operated in reference to last statistic room temperature data and a set temperature inputted and set by a man-machine basis.

CONSTITUTION: A central control device 2 is provided with an air conditioning operation temperature determining part 2-2 for determining an operation target temperature under an actual operation of the air conditioner in reference to an indoor temperature statistic data base 2-1 accumulating last indoor temperature taken from a plurality of temperature sensors 1 in a unit of one day for one year and a room temperature set by a man-machine reference temperature setting part 3. An operating temperature of the air conditioner is determined in response to the accumulated indoor temperature statistic data base. For example, a room temperature of a specific day on the basis of the statistic data of an area C on July 31 is compared with a set temperature input set from the man-machine reference temperature setting part, resulting in that a poor follow-up characteristic is found for the set temperature in reference to the case of ON of the air conditioner and another case of a certain time range. In order to correct this part, if the set temperature is temporarily decreased when the air conditioner is ON and when the temperature starts to increase its value, it is possible to improve a follow-up characteristic for the set temperature.