| 摘要 |
The facsimile device is provided with a facsimile circuit, a voltage detector that detects a voltage of the public line, an open-circuit voltage detector that detects an open-circuit voltage, a telephone status monitoring unit configured to judge whether the external telephone closes the public line, and a warning unit. If a voltage difference between a reference voltage and the open-circuit voltage is smaller than a predetermined voltage difference, the telephone status monitoring unit operates to judge that the external telephone releases the public line if a voltage difference between the reference voltage and a detected line voltage is smaller than the predetermined voltage difference, and to judge that the external telephone closes the public line if the voltage difference between the reference voltage and the detected line voltage is larger than or equal to the predetermined voltage difference. If the voltage difference between the reference voltage and the open-circuit voltage is larger than or equal to the predetermined voltage difference, the telephone status monitoring unit operates to judge that the external telephone releases the public line if the voltage difference between the reference voltage and the detected line voltage at a time when the facsimile circuit has released the public line is smaller than the predetermined voltage difference or if the detected line voltage at a time when the facsimile circuit has released the public line is equal to the open-circuit voltage, and to judge that the external telephone closes the public line if the voltage difference between the reference voltage and the detected line voltage at a time when the facsimile circuit has released the public line is larger than or equal to the predetermined voltage difference and if the detected line voltage at a time when the facsimile circuit has released the public line is different from the open-circuit voltage.
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