A control method of controlling locking or unlocking of storage using a blockchain, the control method comprising: authenticating, when first request information indicating a lock/unlock request is received from a terminal (21, 22), a user of the terminal by using identification information of the terminal and a public-key infrastructure, PKI, determining whether or not a keyholder identified by keyholder information stored in the blockchain matches the authenticated user of the terminal (21, 22) that has transmitted the first request information, by determining whether or not the keyholder information matches information that indicates the user of the terminal that has transmitted the first request information, the lock/unlock request being a lock request or an unlock request, the keyholder information indicating a person having authority to lock or unlock the storage; performing lock/unlock processing when the keyholder is determined to match the user, the lock/unlock processing being processing for causing the storage to lock or unlock in accordance with the first request information, the lock/unlock processing including transmitting a lock/unlock instruction to the storage via a network to cause the storage to lock or unlock without a consensus reaching processing; and performing first storage processing that includes consensus reaching processing performed by a plurality of servers that store transaction data in the blockchain after the lock/unlock processing is performed, the first storage processing being processing of storing, in the blockchain, the transaction data indicating that the lock/unlock processing has been performed. authenticating, when first request information indicating a lock/unlock request is received from a terminal (21, 22), a user of the terminal by using identification information of the terminal and a public-key infrastructure, PKI, determining whether or not a keyholder identified by keyholder information stored in the blockchain matches the authenticated user of the terminal (21, 22) that has transmitted the first request information, by determining whether or not the keyholder information matches information that indicates the user of the terminal that has transmitted the first request information, the lock/unlock request being a lock request or an unlock request, the keyholder information indicating a person having authority to lock or unlock the storage; performing lock/unlock processing when the keyholder is determined to match the user, the lock/unlock processing being processing for causing the storage to lock or unlock in accordance with the first request information, the lock/unlock processing including transmitting a lock/unlock instruction to the storage via a network to cause the storage to lock or unlock without a consensus reaching processing; and performing first storage processing that includes consensus reaching processing performed by a plurality of servers that store transaction data in the blockchain after the lock/unlock processing is performed, the first storage processing being processing of storing, in the blockchain, the transaction data indicating that the lock/unlock processing has been performed.