A locking and unlocking system includes: a server; a mobile terminal; and a key unit, wherein the server includes a server transmission unit configured to transmit cancel information, wherein the mobile terminal includes a terminal transmission unit configured to transmit first authentication information and a first request signal, wherein the key unit includes: a key-unit first reception unit configured to receive the cancel information; a key-unit second reception unit configured to receive the first authentication information and the first request signal; a first authentication unit configured to authenticate the mobile terminal; and a locking and unlocking processing unit configured to perform a process of unlocking or locking the door of the vehicle or facility, and wherein the locking and unlocking processing unit is configured to prohibit unlocking of the door of the vehicle or facility.