1. A storage system, comprising: a processor; a data writing unit implemented on the processor for storing actual data configuring storage data to be written into a storage device and, every time a content of the storage data is updated, newly storing actual data configuring the updated storage data into the storage device; and a data specifying unit implemented on the processor for specifying latest storage data among same storage data stored in the storage device, wherein: the data writing unit is configured to store actual data configuring the storage data into the storage device in association with update information whose value increases by 1 every time the storage data is updated; the data specifying unit is configured to check whether the update information whose value is 2 i (i represents an integer equal to or more than 0) exists in the storage device in an increasing order of a value of i, specify a largest value of the existing update information from among values between a largest value of 2 i that the corresponding update information exists and a value of 2 i+1 , and specify storage data configured by actual data associated with the largest value of the update information, as the latest storage data; and the data specifying unit is configured to: set the largest value of 2 i that the corresponding update information exists in the storage device as first update information, and also set the value of 2 i+1 as second update information; execute an update information search process of checking whether the update information corresponding to an intermediate value between the first update information and the second update information exists in the storage device; execute an intermediate value replacement process of setting the intermediate value as the first update information when the update information corresponding to the intermediate value exists in the storage device, whereas setting the intermediate value as the second update information when the update information corresponding to the intermediate value does not exist in the storage device; and specify the largest value of the update information existing in the storage device by repeatedly executing the update information search process and the intermediate replacement process, and the storage system further comprising: a data deleting unit implemented on the processor for deleting the actual data configuring the storage data that is not the latest and the update information associated with the actual data from the storage device, wherein: the data specifying unit is configured to specify the update information that has been searched at the time of specification of the largest value of the update information and that is corresponding to the value of 2 i existing in the storage device, as non-deletion target update information; the data deleting unit is configured to exclude the update information specified as the non-deletion target update information from information to be deleted from the storage device; and the data specifying unit is configured to, when storage data, configured by the actual data associated with a smaller value of the update information than the largest value of the update information existing in the storage device, is being accessed: include access target update information in the non-deletion target update information, wherein the access target information is: the update information associated with the actual data configuring the storage data being accessed, and the update information that is searched when the data specifying unit specifies the access target update information as the largest value of the update information and is specified as the non-deletion target information.