A storage device and a data processing method of the storage device are provided which can prevent leaking of data attributed to stealing or taking out of a disk device. The storage device includes: disk adapters, each connected to HDDs which constitute one or more RAID groups; and a management part which manages a storage area provided by the HDDs in a state that the storage area is divided into logical storage areas, and manages the RAID groups. The management part sets an encryption state indicative of whether or not the data is to be encrypted with respect to the RAID groups when all of the disk adapters are connected to the HDDs which belong to the RAID groups are encryption adapters. The management part also encrypts, based on the encryption state set with respect to the RAID groups, and stores the encrypted data in the HDD.