Frequency comparison means compares the levels of uplink (UL) and downlink (DL) frequencies which are designated by frequency designation means. When it is determined that the UL frequency is lower than the DL frequency, heterodyne switching means enables a receiving unit to perform frequency conversion using a lower-side heterodyne system and signal processing is performed, using one baseband signal and the other baseband signal obtained by a quadrature demodulation process as an in-phase component and a quadrature component, respectively. When it is determined that the UL frequency is higher than the DL frequency, the heterodyne switching means enables the receiving unit to perform the frequency conversion using an upper-side heterodyne system and signal processing is performed, using the one baseband signal and the other baseband signal obtained by the quadrature demodulation process as the quadrature component and the in-phase component, respectively.