Abstract: For improving, when performing road-vehicle communication or vehicle-vehicle communication between a roadside device and in-vehicle devices or therebetween, efficiency of distribution information verification including digital signature verification and freshness verification, there are included a memory unit that stores, as an authentication information history, a history of second authentication information of communication data which was received in the past from another communication device and which includes first authentication information, distribution information, and the second authentication information and an authentication processing unit that verifies, on the basis of the first authentication information of new communication data being newly received communication data, authenticity of the second authentication information of the new communication data and that compares the second authentication information of the new communication data with the authentication information history stored in the me