A cache device connected to a storage device and connected to a plurality of sources, including a cache unit that relays a read request and a read response between a source and a storage device, and a storage area control unit that stores the source as a first history in association with specification of first data in a read request, and, if the first data are not retained by the cache unit and a storage area sufficient for retaining the first data does not exist, selects data associated with a less number of the sources in the first history as second data in preference to data associated with a greater number of the sources out of the first data or data retained by the cache unit, and, if the second data differ from the first data, causes the cache unit to discard the second data and then store the first data.