An in-vehicle communication device is an in-vehicle communication device that performs a relay process of relaying data between functional units in an in-vehicle network, and includes a communication unit that performs the relay process using correspondence information indicating a correspondence relation between an Internet protocol (IP) address and a media access control (MAC) address of one or more functional units, an address managing unit that generates the correspondence information, and an authenticating unit that performs an authentication process for the functional unit, in which the authenticating unit performs the authentication process for the functional unit in which an IP address and a MAC address are newly registered in the correspondence information by the address managing unit, and the address managing unit deletes the correspondence relation of the functional unit from the correspondence information when the authentication process for the newly registered functional unit is not successfully performed.