A vehicular electronic control unit that transmits a message or a file acquired from a vehicle-external device to an electronic control unit in a vehicle is provided. The vehicular electronic control unit performs vehicle-external communication with the vehicle-external device and performs vehicle-internal communication with the electronic control unit. The vehicular electronic control unit converts an SOVD format in the vehicle-external communication to an SOVD-noncompliant format when the vehicle-external communication is data communication compliant with SOVD communication specifications and a delivery destination of the message or the file based on the SOVD format is an SOVD-noncompliant electronic control unit. The vehicular electronic control unit generates a delivery sequence for managing an order in which messages are delivered, according to the SOVD-noncompliant format obtained via converting the SOVD format and performs the vehicle-internal communication according to the generated delivery sequence.