A signal processing device, which is more practical for restoring signals, includes a signal processing unit for processing a signal. The processing unit produces restored data that approaches the original signal data before fluctuating (before blurring) by repeating the following processing: generating comparison data Io′ from arbitrary signal data Io by using information data G regarding fluctuation factors that triggers signal fluctuation; comparing the comparison data Io′ with original signal data Img′ as an object to be processed thereafter; producing restored data Io+n by allocating difference data δ to the arbitrary signal data Io while using the information data G regarding fluctuation factors; and substituting the restored data Io+n for the arbitrary signal data Io thereafter.