A control method includes: receiving first information pertaining to a first contract from a first terminal used by a first user who is one of two parties who have agreed to the first contract; when consent of a party aside from the two parties is required to validate the first contract, identifying a second user as the party aside from the two parties with reference to a ledger storing information pertaining to a past contract, and transmitting the first information to a second terminal operated by the second user; obtaining second information in which a confirmation result indicating whether the second user consents to the first contract and a digital signature of the second user are added to the first information; and confirming the second information, and when the confirmation result indicates consent, setting the first contract as a valid contract and storing the second information in the ledger.