PURPOSE: To provide a cache controller which can suppress the stored area of a cache memory from becoming a fragment.

CONSTITUTION: A pattern data update means 21 updates the content of the cache memory 10 based on the content of information showing the use situation of the cache memory in a cache memory use situation storage means 25 and that of information showing the use situation of pattern data in a pattern data management information storage means 23. The pattern data update means 21 decides whether the fragmentation of the stored area in the cache memory reaches a state which is previously set or not. A pattern data compaction means 22 executes a compaction processing for the cache memory 10 when the pattern data update means 21 decides that the fragmentation of the stored area of the cache memory 10 reaches the previously set state.