PURPOSE: To reduce a storage capacity, by stopping sampling intermittently when an analog signal is sampled with a certain sampling frequency to store its sample value.

CONSTITUTION: The analog signal is sampled at sampling timings t1Wt25 of a certain period, and sampled signal values S(t1)WS(t24) are stored. The sampling is stopped at sampling times T5, t10, t15, and t20. In case that stored data is called to reproduce sample values S(t5), S(t10), S(t15), and S(t20), they are obtained by interpolation between sample values before and after the stop of sampling, for example, the sample value S(t5) is obtained by interpolation between sample values S(t4) and S(t6). By this storage method, the storage capacity is reduced with the same sampling frequency.