Patent ID: 7787156

Claim:
A facsimile device connected to a public line in parallel with an external telephone, comprising: a facsimile circuit configured to send and receive image data through the public line; a terminal to which the external telephone can be connected, the terminal connecting the external telephone to the public line in parallel with the facsimile circuit; a line switch unit configured to connect the public line to the terminal when operated by a manual operation; a judgment unit configured to judger whether a signal coming to the facsimile device through the public line is a sound signal or a facsimile signal; a warning indication unit configured to output a warning message to operate the line switch unit if the judgment unit judges that the signal coming to the facsimile device through the public line is the sound signal; a voltage detector that detects a voltage of the public line; a telephone status monitoring unit configured to judge whether the external telephone closes the public line based on the voltage of the public line detected by the voltage detector and a reference voltage; a warning unit configured to output a warning indicating that the external telephone is in a busy state if the telephone status monitoring unit judges that the external telephone closes the public line; and a first monitoring operation control unit configured to keep the telephone status monitoring unit in an inactive state until a predetermined time elapses from a time when the facsimile circuit releases the public line, and to activate the telephone status monitoring unit if the predetermined time elapses from the time when the facsimile circuit releases the public line, wherein only when the line switch unit is operated by the manual operation, the first monitoring operation control unit activates the telephone status monitoring unit even if the predetermined time does not elapse from the time when the facsimile circuit releases the public line.