An information storage device (30, 200, 710) comprising a memory (220, 320) for storing data and a controller for performing access control on the memory, wherein the controller is configured to lock the memory to validate access control on the memory, in response to a command input from an information processing apparatus (20, 310, 510) the controller is configured to unlock the memory to remove the access control, in response to a command input from the information processing apparatus (20, 310, 510), and the controller is configured to store lock status data prior to the memory being unlocked in storage means (213, 320), the lock status data including an identifier, ID, of the information processing apparatus (20, 310, 510) having output a lock request and, when the information storage device is turned off and then on, the controller is configured to recreate a lock status of the memory (220, 320) on the basis of the lock status data stored in the storage means (213, 220) and to perform memory access control based on the recreated lock status, including the ID, wherein the controller is configured to perform processing in response to an unlock request from the information processing apparatus (20, 310, 510) on the basis of the lock status recreated when the information storage device is turned on again, the controller is configured to perform verification of a key set including the ID of the information processing apparatus (20, 310, 510) having output the unlock request or the lock request and, provided that the verification succeeds, to perform unlocking based on the unlock request or locking based on the lock request, the controller is configured to generate a random number, to transmit the generated random number and the stored ID of the information processing apparatus (20, 210, 510, 720) having output the lock request to the information processing apparatus (20, 210, 510) and to receive, from the information processing apparatus (20, 310, 510), encrypted data [E(LK, Rms)] generated by encrypting a random number, Rms, on the basis of a lock key, LK, held by the information processing apparatus, the key set is a key set [ID, LK] consisting of the ID held by the information processing apparatus and the LK associated with the ID, the information storage device (30, 200, 710) has a lock master key, LMK, that is applicable to compute the LK, which is a hash value based on the relationship LK = H(LMK, ID), the hash value being computed for the ID by applying the LMK, and in response to the lock request the controller is configured to verify the key set held by the information processing apparatus (20, 310, 510) having output the lock request by generating the Rms and transmitting it to the information processing apparatus (20, 310, 510), by receiving the ID and the encrypted data [E(LK, Rms)] from the information processing apparatus (20, 310, 510), by computing LK = H(LMK,ID) and [E(LK, Rms)], and by comparing the received [E(LK, Rms)] with the computed [E(LK, Rms)], and in response to the unlock request the controller is configured to verify the key set held by the information processing apparatus (20, 310, 510) requesting unlocking by generating the Rms and transmitting it and the stored ID of the information processing apparatus (20, 210, 510) having output the lock request to the information processing apparatus (20, 310, 510) requesting unlocking, by receiving the encrypted data [E(LK, Rms)] from the information processing apparatus (20, 310, 510) requesting unlocking, by computing LK = H(LMK,ID) and [E(LK, Rms)], and by comparing the received [E(LK,Rms)] with the computed [E(LK, Rms)].