A locking and unlocking system includes a portable terminal and a server. The portable terminal includes a service providing unit, a first sending unit, and a first receiving unit. The service providing unit provides a use reservation service for a vehicle or facilities by communicating with another server. The first sending unit sends a first signal to the server in response to a request from the service providing unit. The first signal requests authentication information used for locking and unlocking. The first receiving unit receives the authentication information from the server. The server includes a second receiving unit and a second sending unit. The second sending unit sends a second signal including the authentication information to the portable terminal when the second receiving unit receives the first signal.