PURPOSE: To adjust the frequency characteristic automatically in such a way that no drift nor adjustment error takes place and limitation with respect to a reference signal is less.

CONSTITUTION: A switch SW is used to select a signal to be filtered or a reference signal from a reference signal generating circuit 10 for a filter circuit 11 whose characteristic is externally controlled and having a function of generating two signals having a phase difference of 0° and 90° with respect to an input signal. A current of a current source IB is controlled based on the result of phase comparison by a phase comparator circuit 12 receiving the two signals from the filter circuit 11. A D/A converter (DAC) circuit 13 outputs a decode bias in proportion to a current from the current source IB to control the characteristic of the filter circuit 11. A decode value control circuit 14 selects a decoded value of the DAC circuit 13. A timing pulse PA is used to switch the state of the DAC circuit 13, the phase comparator circuit 12 and the switch SW.