To allow long-term saving of digital data, such as videos or speech.

Input digital data, such as videos or speech, are successively stored in a memory section 3 and are accumulated. A control section 7 monitors the memory section 3 and when the free capacity of the memory section 3 attains a predetermined capacity or when a timer section 5 clocking the lapse time after the memory section 3 starts storage, the data are read out successively in the order in which the data are stored from the memory section 3 and the processing to decrease the data quantity is performed in a data processing means 4. Which of the free capacity or the lapse time is to be used as a reference is preferably set by a processing reference setting means 6a. There is a mode shown in Figure in addition to a data compression processing mode 4a as the modes of the processing of the processing means 4 described above and these modes are previously set by a video processing setting section 6b and a speech processing setting section 6c. The data processed in the processing means 4 are converted to the data prior to the processing and are restored in the memory section 3.