A communication apparatus for communicating with both of a vehicle control device, which performs vehicle control preliminary set in a vehicle when authentication with an authentication device carried by a user is successful, and a portable device, which functions as the authentication device, the communication apparatus also functioning as the authentication device, the communication apparatus includes: a to-portable-device communicator that performs wireless communication with the portable device when performing authentication with the vehicle control device; and an authenticator that performs authentication with the vehicle control device when wireless communication with the portable device is established.