b are operated in the microphone operation mode operation parameters for conducting acoustic inputting are set in them at the time of operation in the receiver operation mode operation parameters for conducting voice output with a volume suitable for receiving operation in which the user brings the rec 13 into contact with an ear are set at the time of operation in a speaker operation mode parameters for outputting voice with a volume suitable for the user facing the portable telephone 101 as in video phones are set in this speaker operation mode a greater clearer voice output as compared with the above described receiver operation mode is demanded accordingly a greater output gain is set and a low frequency band in frequency characteristics is set to become high when the above described initialization processing is completed the cpu 24 in the communication processing unit 20 monitors the operation state of the portable telephone 101 according to the state the cpu 24 specifies an operation mode of the acoustic input output unit 10 to the acoustic processing unit 50 step s 3 for example when the user starts typical talking i e talking using only voice by using the portable telephone 101 step s 3 a the cpu 24 orders the acoustic processing unit 50 to bring one of the mic 15 a and the mic 15 b operate into the microphone operation mode and bring the other of the microphones and the spk 11 into an off mode i e stop their operation step s 4 at the time of ordinary talking.