In the present invention, time information is sent through a common power line in executing home automation devices or using various industrial equipments. In the power line broadcasting, a small amount of data, such as time information, is transmitted unidirectionally, and long-distance power line broadcasting can be possible using carriers of a low frequency band. time setting for various instruments is automatically performed in response to a power signal after a breakdown of electric current, making unnecessary a user's action to perform the time setting, and the existing power line can be used without change.