A wireless communication system comprising: an in-vehicle unit mounted on a vehicle and comprising an operation unit that can be arbitrarily operated by an occupant, the in-vehicle unit capable of wirelessly transmitting an access signal when the operation unit is operated; a portable device, which can be carried by the occupant, capable of wirelessly transmitting a vehicle-specific authentication code on a condition that the access signal is received; and a determination unit capable of determining whether or not the authentication code is a regular authentication code on a condition that the authentication code is received; wherein start of a driving source of the vehicle is permitted or running of the vehicle is enabled when the determination unit determines that the authentication code is the regular authentication code; and wherein a security mode in which a function of transmitting the access signal by the in-vehicle unit or a function of transmitting the authentication code by the portable device is stopped can be set by a predetermined setting operation; wherein the security mode can be released when a specific releasing operation is performed on the operation unit provided in the in-vehicle unit; or wherein the security mode can be released when a specific releasing operation is performed on an operation unit provided in the portable device; when the security mode is set, random number codes are generated and stored in a storage unit of the in-vehicle unit and a storage unit of the portable device, respectively; and when the releasing operation is performed, the random number code stored in the storage unit of the portable device is compared with the random number code stored in the storage unit of the in-vehicle unit, and the security mode is released only when the random number codes match. an in-vehicle unit mounted on a vehicle and comprising an operation unit that can be arbitrarily operated by an occupant, the in-vehicle unit capable of wirelessly transmitting an access signal when the operation unit is operated; a portable device, which can be carried by the occupant, capable of wirelessly transmitting a vehicle-specific authentication code on a condition that the access signal is received; and a determination unit capable of determining whether or not the authentication code is a regular authentication code on a condition that the authentication code is received; wherein start of a driving source of the vehicle is permitted or running of the vehicle is enabled when the determination unit determines that the authentication code is the regular authentication code; and wherein a security mode in which a function of transmitting the access signal by the in-vehicle unit or a function of transmitting the authentication code by the portable device is stopped can be set by a predetermined setting operation; wherein the security mode can be released when a specific releasing operation is performed on the operation unit provided in the in-vehicle unit; or wherein the security mode can be released when a specific releasing operation is performed on an operation unit provided in the portable device; when the security mode is set, random number codes are generated and stored in a storage unit of the in-vehicle unit and a storage unit of the portable device, respectively; and when the releasing operation is performed, the random number code stored in the storage unit of the portable device is compared with the random number code stored in the storage unit of the in-vehicle unit, and the security mode is released only when the random number codes match.