COMMUNICATION SYSTEM AND IN-VEHICLE COMMUNICATION APPARATUS

Provided is a communication system in which an in-vehicle communication apparatus mounted in a vehicle is capable of acquiring update information of a system configuration relating to issuance of certificate information, and an in-vehicle communication apparatus that is included in this communication system. An in-vehicle communication apparatus mounted in a vehicle acquires update information related to an increase or decrease in the system configuration of a certificate information issuing system from an update information distribution server apparatus, via a roadside communication apparatus installed on a road. The in-vehicle communication apparatus, in a case of becoming communicable with the roadside communication apparatus, acquires function list information from the roadside communication apparatus, and determines whether this roadside communication apparatus has a relay function. The in-vehicle communication apparatus acquires update information from the update information distribution server apparatus periodically in a predetermined cycle, such as daily, weekly or monthly, for example.