Abstract: A modulation-demodulation apparatus of a relatively simple arrangement is able to prevent a bad influence caused due to interference between two local oscillators and a portable wireless communication apparatus uses this modulation-demodulation apparatus. In a modulation-demodulation apparatus using a local oscillator (105) for use in direct conversion type of a receiving system and a local oscillator (104) for use with a transmitting system, a ratio (C/D) between a reception frequency and an oscillation frequency of the reception local oscillator (105) and a ratio (A/B) between a transmission frequency and an oscillation frequency of the transmission local oscillator are made different from each other.