A variable divider in which a dividing number setting parameter can be set is provided in a reference oscillator. And, when a frequency setting parameter is selected to that a DDS will not output a spurious at a specified level or at a level higher than the specified level within an output band of an PLL in response to an output frequency from the PLL, both a conversion function setting parameter for a variable divider in the PLL and a dividing number setting parameter for a variable divider in the reference oscillator are adjusted so that the output frequency and the selected frequency setting parameter are satisfied.
