PURPOSE: To eliminate the need of providing time integrators for respective air conditioners so as to reduce cost by calculating the operation time of the respective air conditioners as operation parameters from the state change of plural units to be operated, the air conditioners, for example, and from change time and accumulating it.

CONSTITUTION: The selection circuit 13 of a detection terminal unit 10A connected to the respective air conditioners 3a-3n switches the input gate of an input circuit 11 at every prescribed time and detects the state of respective switches 4a-4n at every prescribed sampling time. A state change detection circuit 14 detects the change of the opening/closing state of the switches and outputs the detection signal to an arithmetic processing unit 20 through a report circuit 15. In the arithmetic processing unit 20, a subtraction circuit 24 and an addition circuit 25 calculate operation time for the respective air conditioners, and the operation time is accumulated in an operation time storage circuit 26. The operation time of the respective air conditioners 3a-3n, which is thus obtained, is accessed by a selection circuit 27 obtaining a reading signal from a reading circuit 21, is displayed in a display device 28 and is recorded in a recording device 29.