Proposed is an apparatus and method of preventing the leakage of information from an external storage apparatus even when such external storage apparatus is stolen or accessed from an unauthorized host computer. This external storage apparatus accessible from a host computer or another external storage apparatus via a network encrypts or decrypts data written from a host computer to be stored in the storage area, sends a request for existence confirmation to the host computer or the other external storage apparatus every predetermined period of time, and zeroizes an encryption key to be used in the encryption calculation for encrypting or decrypting data to be performed by the encryption calculation unit based on the result of a response from the host computer or the other external storage apparatus in reply to the request.