Authentication data communication system for a vehicle, power coupling device for a vehicle, data communication system for a vehicle and data communications apparatus for a vehicle

A vehicle data communication system is disclosed. The vehicle data communication system comprises an authentication means (102d, 103d, 104c, 109a) for authenticating an external device (105) which is connected to a bus (106), an authentication control means (102e, 103e, 104d) for determining if an external device ( 105) by the authentication means (102d, 103d, 104c, 109a) is authenticated, and for setting an authenticated state in order, between the external device (105) and an access target ECU (104) to the bus (106) after determining that the external device (105) by the authentication means (102d, 103d, 104c, 109a) is authenticated to allow data communication, and an authentication maintaining means (102h, 103h, 104g) for maintaining the authenticated state within a predetermined period after the authenticated state (, 104d 102e, 103e) is set by the authentication control device, on.