A sweeping signal generating device, comprising: a first converter including a D/A converter configured to convert digital signals received from a controller into analog signals and output a sweeping signal having a first offset value added to or subtracted from a sweeping standard level; a second converter including a D/A converter configured to convert digital signals received from the controller into analog signals and output an offset signal having a second offset value corresponding to the first offset value; an adder circuit configured to add the sweeping signal output from the first converter and the offset signal output from the second converter; and the controller including one or more processors configured to determine the first offset value and the second offset value so that nonlinearity of each of the sweeping signals caused by nonlinear noise superimposed on each of the sweeping signals is smaller than nonlinearity when at the standard level, wherein the first converter is configured to output the sweeping signal having the first offset value determined by the controller across at least one cycle, wherein the second converter is configured to output the offset signal having the second offset value determined by the controller across the at least one cycle, and wherein the sampling rate of the D/A converter of the second converter is sufficiently lower than the sampling rate of the D/A converter of the first converter, and the nonlinear noise superimposed on the offset signal output from the second converter is sufficiently small when compared to the nonlinear noise superimposed on the sweeping signal. a first converter including a D/A converter configured to convert digital signals received from a controller into analog signals and output a sweeping signal having a first offset value added to or subtracted from a sweeping standard level; a second converter including a D/A converter configured to convert digital signals received from the controller into analog signals and output an offset signal having a second offset value corresponding to the first offset value; an adder circuit configured to add the sweeping signal output from the first converter and the offset signal output from the second converter; and the controller including one or more processors configured to determine the first offset value and the second offset value so that nonlinearity of each of the sweeping signals caused by nonlinear noise superimposed on each of the sweeping signals is smaller than nonlinearity when at the standard level, wherein the first converter is configured to output the sweeping signal having the first offset value determined by the controller across at least one cycle, wherein the second converter is configured to output the offset signal having the second offset value determined by the controller across the at least one cycle, and wherein the sampling rate of the D/A converter of the second converter is sufficiently lower than the sampling rate of the D/A converter of the first converter, and the nonlinear noise superimposed on the offset signal output from the second converter is sufficiently small when compared to the nonlinear noise superimposed on the sweeping signal.