A facsimile apparatus, to which an external telephone enables to be
connected through a line, has a line I/F section that transfers and
receives signal through a network, a voltage detection section that is
provided in a semiconductor DAA and detects a line voltage of the line,
an adjustment section that adjusts a line voltage during establishment of
a connection through the line so as to be within a predetermined voltage,
and an external telephone monitor section that acquires a value of the
line voltage detected by the voltage detection section at regular time
intervals and monitors a use state of the external telephone based on the
acquired values of the line voltage.