PURPOSE: To suit the air conditioning to the condition of the room by adjusting the operation of an air conditioner according to the count by a person detector which keeps count of the occupants.

CONSTITUTION: By selecting automatic operation for keeping count of the occupants by a person detector 12 and operating an air cleaner 1 a 1min timer is started and the person detector 12 starts counting the number of times of the detection within the 1min period. When the number of times of the detection counted is determined at 0, the counting is initialized and repeated for another 1min period. A low speed is selected for the operation if the detection is one to four times and a high speed is selected if the detection is give times a more, and the operation is continued in either of these selected modes for 20min with a 20min timer counting the time. While the 20min timer is counting the time, the person detector 12 is set working with start of the 1min timer in parallel with the 20min timer so that, if there is a count by the person detector 12, the 20min timer is reset and, according as the detection is determined at one to four times or five times or more, the mode in which the operation is continued is selected again. If there is no count by the person detector 12 during the 20min, the operation is stopped and initialized.