| 摘要 |
PURPOSE:To avoid the continuation of an off-hook state by allowing an extension telephone set provided separately to execute an alarm incoming display, when some telephone set continues an off-hook state exceeding a prescribed time. CONSTITUTION:When an extension telephone set 151 is brought to off-hook, it is detected by a line circuit 142, and it is connected to an originating register trunk 141 through a network. When this state exceeds a prescribed time, a central control unit 111 discriminates it by the operation of a timepiece circuit 1221, releases the originating register trunk 141, reads out incoming destination information (the telephone number of a telephone set 153) registered in advance in a storing circuit 131, calls the telephone set 153 by connecting a call signal 162 to the incoming destination telephone set 153, and informs the telephone number of the telephone set 151 of an off-hook state.
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