A control system for a vehicle includes a portable authentication terminal configured to authenticate a user who carries the portable authentication terminal, and a vehicle configured to communicate with the portable authentication terminal. The vehicle includes a sound generation unit configured to generate a predetermined sound within a vehicle cabin, an information reception unit configured to receive information transmitted from the portable authentication terminal, and a determination unit configured to determine whether the portable authentication terminal is within the cabin based on the received information. The portable authentication terminal includes a sound collection unit configured to collect a sound, and an information transmission unit configured to transmit information based on the collected sound to the vehicle. The determination unit is configured to determine whether the portable authentication terminal is within the cabin based on whether the received information is information based on the sound generated by the sound generation unit.