A frequency signal generator includes a controller for generating a frequency generation signal, a reference frequency signal generator for generating a first frequency signal and generate a second frequency signal by dividing a first frequency signal from the controller, an assistance frequency signal generator adapted to generate a third, fourth, and fifth frequency signals and to output a sixth frequency signal in response to an assistance frequency select signal, a mixer for selecting a sign of the sixth frequency signal in response to a sign select signal and generating a seventh frequency signal and a eighth frequency signal by mixing the sixth frequency signal of the selected sign and the first frequency signal, a switch adapted to output the seventh or eighth frequency signal in response to a dividing select signal, and a first divider outputting a ninth frequency signal by dividing the eighth frequency signal from the switch.