| 摘要 |
PROBLEM TO BE SOLVED: To provide a trunk line state detection device which can always precisely detect various trunk line states with inexpensive constitution. SOLUTION: A forward polarity detection circuit 13 and an opposite polarity detection circuit 14, which are connected in parallel between two wires 11 and 12 connected to trunk lines A and B, and a trunk line state detection means 15 detecting a trunk line state based on the outputs of the forward polarity detection circuit 13 and the opposite polarity detection circuit 14 are installed.
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