PURPOSE: To attain sure polling communication independently of timing of depression of a start button by providing a means detecting a received signal having a prescribed frequency and a means measuring the length of the received signal so as to discriminate the kind of the received signal after an initial identification signal is transmitted.

CONSTITUTION: When a signal of 2,100Hz is received by a 2,100Hz signal detecting circuit 15, a timer circuit 17 set to 4sec is started. If the signal is interrupted before the time of the timer circuit 17 is over, it is decided that signal of 2,100 Hz is a CED (called station identification signal) to transmit an NSF signal (non-standard device signal) and a DIS signal (digital identification signal) again. When the phase matching of 9Hz is finished by a phase matching detection circuit 16, the mode moves to the standard mode communication of a mini-fax. When the phase matching of 6Hz is finished by the phase matching detection circuit 16, a timer circuit 18 set to 6.5sec at the point of time is started. If the signal is interrupted within 6.5sec, the communication of the mini-fax with high quality mode is attained.