PURPOSE: To make it possible to efficiently compress long data containing repeated patterns, by selecting the max. value as the characteristic of a pattern, and using the same as a trigger to accumulate the gathering of the max. value in time series memory on the basis of the trigger outputted at the max. value.

CONSTITUTION: When data compression is performed, a data selector S1 selects the run-length code from a transition interval counter and, when a compression flag erects in the read data of main memory 6 at the time of data regeneration, the content of a third register R3 is selected. When the compression flag is not erected in the read data of the main memory 6 at the time of data regeneration, the read data of the main memory 6 is selected to be sent to a first register R1. When it is shown that the output of a max. value detecting circuit 9 detects a max. value, a data selector S3 selects the content of max. value address memory 8 but selects the content of a time series memory address counter 10 when the max. value is not detected.