The speed of recording or reproduction of data to or from an HDD in an information processor is increased. This is achieved without an increase in device size, system changes, or other inconvenience. A cache memory configured by, for example, a flash memory for the data to be recorded to or reproduced from the HDD is provided not on the HDD side but on the ODD side. When, after the HDD has been replaced, there is inconvenience in using this cache memory as a cache for the data to be recorded, the cache memory is used only as a cache for the data to be reproduced, and if data in the cache memory and data on the HDD do not match each other, the cached data is invalidated.