PURPOSE: To increase transmission speed of a data and a control signal, and to quickly control an indoor environment to make a comfortable environment, by transmitting plural bits in synchronizing with the frequency of a power source of an air conditioner.
CONSTITUTION: When a power source switch of an air conditioner is turned on, a controller 10 of an indoor machine outputs data, a control signal, and a serial signal of, for instance, 8 bits (01101001), corresponding to a set value which is set by an operation switch by a timing of a synchronizing signal pulse, to a controller 11a. On the other hand, a controller 11 of an outdoor machine converts its serial signal (01101001) by a timing of the synchronizing signal pulse and inputs it. In such a way, between the controllers 10, 11 of the indoor machine and the outdoor machine, the serial signal of plural bits is sent and received by a timing of a synchronizing signal pulse generated by synchronizing with a frequency of a power source. Accordingly, the transmission speed between the indoor machine and the outdoor machine can be increased. In such a way, a compressor, etc., of the outdoor machine can be allowed to respond quickly, and the indoor environment can also be controlled quickly.