PURPOSE: To enable accurate frequency measurement by dividing an input signal, converting the signals obtained into sampled and coded signals, and using discrete Fourier transform(DFT) technique on them.

CONSTITUTION: An input signal is first divided by a divider into a plurality of synchronous signals, which are added to L sampler/decoder devices 200. The sampler/decoder devices 200 sample the synchronous signals at different frequencies, and perform analog-to-digital conversion to convert the plurality of synchronous signals into coded signals. Next, a processing element 210 performs DFT on the individual coded signals, and accesses a decoding or memory storage device in which, in respective storage positions, the values of DFT corresponding to the binary expression of the addresses of the storage positions are stored. Then a logic circuit 220 combines the results of DFT on the individual signals to measure the frequency of the input signal.