A device includes a facsimile circuit, a voltage detector, an open-circuit voltage detector, and a telephone status monitoring unit. If a first voltage difference is less than a predetermined voltage difference, the monitoring unit judges that the public line is released if a second voltage difference is less than the predetermined difference, and that the public line is closed if the second difference is not less than the predetermined difference. If, when the facsimile circuit has released the public line, the first difference is not less than the predetermined difference, the monitoring unit judges that the public line is released if the second difference is less than the predetermined difference or if the detected line voltage equals the open-circuit voltage, and that the public line is closed if the second difference is not less than the predetermined difference and if the detected line voltage is different from the open-circuit voltage.