A memory cache device in which a storage area used for a memory data protection function is effectively used at the time of not using the memory data protection function. A mode selection signal makes ECC code sections for storing an ECC code function as a storage area for storing ECC codes used for performing error detection or error correction on data stored in data RAMs at the time the memory data protection function is enabled and as a way added to the data RAMs at the time the memory data protection function is disabled.