A cache controller is connected to a processor and a main memory. The cache controller is also connected to a cache memory that can read and write at a speed higher than the main memory. The cache memory is provided with a plurality of cache lines that include a tag area storing an address on the main memory, a capacity area storing a capacity value of a cache block, and a cache block. When a read request is executed from the processor to the main memory, the cache controller checks whether the requested data is present in the cache memory or not. A cache capacity determination unit determines a capacity value for the cache block and supplies to a capacity area.