A communications relay apparatus for relaying communications between an electronic control unit (ECU) connected to the apparatus via an in-vehicle local area network (LAN) and an external device connected to the apparatus via a communication path different from the in-vehicle LAN. In the apparatus, a data transfer unit forwards relay data received from the ECU to the communication path and forwards relay data received from the external device to the in-vehicle LAN. But the data transfer unit is inhibited from forwarding reprogramming data for reprogramming the ECU received from the external device to the in-vehicle LAN. An authentication unit authenticates a vehicle user, and when the vehicle user is successfully authenticated, then permits the data transfer unit to forward the reprogramming data to the in-vehicle LAN.