PURPOSE: To display an analysis result on a common display screen and at the same time improve efficiency of analysis by performing FFT operation processing for a plurality of digital signal trains with different frequency regions which are generated by a common measurement analog signal.

CONSTITUTION: When, for example, a frequency region 60-72.5kHz is to be observed simultaneously while a frequency region 50-100kHz is being observed, namely when the maximum frequency range is set to 100kHz, frequency shift circuits 2 and 20 are set to achieve 7 and 66.25kHz frequency shifts, respectively, a digital filter 3 is set to achieve a cut-off frequency of 25kHz and 6.25kHz, and data thinning circuits 4 and 40 are set to achieve a thinning of 1/4 and 1/16. Then, an FFT operation circuit 5 performs FFT operation and various kinds of analysis operations when a certain number of data (for example 1024 points) are ready, thus displaying a plurality of analysis results at different frequency regions on a common display screen 6 simultaneously and analyzing various kinds of signals efficiently.