The present invention suppresses a harmonic component without impairing the phase orthogonality of a pair of complex signals. A polyphase filter is configured so that K pieces of filter circuits, each of which comprises a resistor and a capacitor, are connected and +360/K degrees out of phase with a preceding one. Since counterclockwise rotation occurs when expression is given in terms of the complex plane, a notch occurs in a negative frequency region. A RC value is set so that a notch occurs in a specified frequency band to suppress a (4N+1)-order harmonic component. Since the polyphase filter has a symmetrical structure, an unbalanced component contained in an input signal is eliminated at a frequency that agrees with a pole determined by the RC value. This action improves the orthogonality.