It is an object to provide a communicating apparatus and its program in which in the case where the RTC pattern or the RCP frame cannot be received due to the noises or in the case where a modem diverges and data cannot be normally demodulated, a procedure signal can be certainly detected, the modem can advance to a low-speed mode, and a possibility of a communication error can be remarkably reduced. During the image reception, both a carrier of V.21ch2 modulation and data signal quality (EQM) in a high-speed mode are, in parallel, monitored. When the data signal quality (EQM) deteriorates to a value larger than or equal to a predetermined threshold value and the carrier of the V.21ch2 modulation is detected, the modem advances to the low-speed mode and the procedure signal is received.