PURPOSE: To set a frequency of a signal fed to a filter to be a filter center frequency at all times by employing a SAW filter and a SAW oscillator for the frequency conversion circuit.

CONSTITUTION: A 2nd local oscillation circuit 20 generates a signal of a 2nd local oscillation frequency based on a SAW oscillator 2 formed on one and same board for a SAW (surface acoustic wave) filter 7. A mixer 22 mixes a signal generated from a PLL oscillator 4 and a signal of the 2nd local oscillating frequency. 1st output signal is outputted via a band pass filter BPF 5 as a signal of the lst local oscillating frequency. The 1st local oscillating frequency signal is generated based on the 2nd local oscillating frequency signal and the 2nd local oscillating frequency signal is used as it is, then the frequency change of the SAW filter 7 and the frequency change of the SAW oscillator 21 are identical and the frequency of the signal fed to the SAW filter 7 is always coincident with the filter center frequency.