1. A storage device, comprising: an address table; a control circuit comprising a RAM (Random Access Memory); a cache memory reserved in the RAM; and a flash memory device that is a storage medium for user data, wherein the control circuit manages access for the flash memory device, the control circuit makes access to the user data on the flash memory device via the address table, in the address table, with an index of an address value generated from an initial logical address, location information of a page group 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 that are segmentation results are stored in the flash memory device, read as required when the user data is accessed, and subsequent to storing and reading the user data is expanded on the cache memory; a second address table, wherein in the second address table, location information of a page is acquired for any of the small address tables on the flash memory device corresponding to the initial logical address, and the control circuit manages access for the user data on the flash memory device, based on the initial logical address, via referring to the second address table and the location information of the page acquired from the corresponding small address table, the location information of the page in the second address table is used to check whether the user data that was subsequently expanded on the cache memory includes a user-desired data, when a cache miss occurs, the user-desired data is read from the flash memory and expanded on the cache memory while the second address table is updated accordingly, and the control circuit refers to the updated second address table, based on the initial logical address, to acquire page location information about the user-desired data, and based on the location information of the page, the user-desired data on the flash memory device is accessed.