A vehicular control system comprising: a vehicle-mounted machine configured to perform first communication and second communication, the first communication being communication according to a first communication technology using radio waves of a first frequency band and the second communication being communication according to a second communication technology using radio waves of a second frequency band; a mobile terminal configured to perform third communication according to a third communication technology different from the first communication technology and the second communication technology; a first key device provided in a vehicle, the first key device being configured to obtain authentication information including an identifier of the vehicle from the mobile terminal using the third communication technology, and operate as a vehicle key of the vehicle specified by the identifier; and a second key device provided in the vehicle, the second key device being configured to receive a first computation result according to the third communication technology, the first computation result being a result of predetermined computation performed by the first key device based on a first signal, and the first signal being transmitted from the vehicle-mounted machine according to the first communication technology, obtain a second computation result by performing predetermined computation based on the first signal and send a second signal to the vehicle-mounted machine according to the second communication technology when the first computation result matches the second computation result. a vehicle-mounted machine configured to perform first communication and second communication, the first communication being communication according to a first communication technology using radio waves of a first frequency band and the second communication being communication according to a second communication technology using radio waves of a second frequency band; a mobile terminal configured to perform third communication according to a third communication technology different from the first communication technology and the second communication technology; a first key device provided in a vehicle, the first key device being configured to obtain authentication information including an identifier of the vehicle from the mobile terminal using the third communication technology, and operate as a vehicle key of the vehicle specified by the identifier; and obtain authentication information including an identifier of the vehicle from the mobile terminal using the third communication technology, and operate as a vehicle key of the vehicle specified by the identifier; and a second key device provided in the vehicle, the second key device being configured to receive a first computation result according to the third communication technology, the first computation result being a result of predetermined computation performed by the first key device based on a first signal, and the first signal being transmitted from the vehicle-mounted machine according to the first communication technology, obtain a second computation result by performing predetermined computation based on the first signal and send a second signal to the vehicle-mounted machine according to the second communication technology when the first computation result matches the second computation result. receive a first computation result according to the third communication technology, the first computation result being a result of predetermined computation performed by the first key device based on a first signal, and the first signal being transmitted from the vehicle-mounted machine according to the first communication technology, obtain a second computation result by performing predetermined computation based on the first signal and send a second signal to the vehicle-mounted machine according to the second communication technology when the first computation result matches the second computation result.