1. A storage device, comprising: an address table; a cache memory; a flash memory device being a storage medium for user data; and a control circuit that is in charge of access management for the flash memory device, wherein the control circuit makes access to the user data on the flash memory device via an address table, in the address table, with an index of an address value generated from an initial logical address, location information is acquired for the user data on the flash memory device corresponding to the index, and the address table is segmented in its entirety into a plurality of small address tables for every area of the index, and the small address tables being segmentation results are stored in the flash memory device, read as required when the user data is accessed, and expanded on the cache memory with entries of the small address tables.