PURPOSE: To obtain modulated wave with a small step frequency from a wide band by selecting a signal obtained by mixing sine wave with a small step frequency using a plurality of local signals while modulating the mixed signal as a carrier signal using a base band signal.

CONSTITUTION: Output sine wave that is output from a DDS circuit 2 is divided into two by a hybrid circuit 3 and the divided two waves are input in mixer circuits 4 and 5, respectively. An analog switch 8 is controlled such that if a carrier signal to be sent is within a range of frequency extracted by a band pass filter 6, the analog switch 8 selects an output of the band pass filter 6, and if the carrier wave is within a range of frequency extracted by a band pass filter 7, the analog switch 8 selects an output of the band pass filter 7. A converter 9 uses a selected carrier signal to carry out modulation using a base band signal, thus outputting a modulated wave Fm.