PURPOSE: To secure the reliability of communication data transmission in multiple address communication.

CONSTITUTION: In the on-vehicle data communication system of a bus system in which at least one master equipment 200 and plural slave equipments 200-1-200-n are connected to the same communication bus 14, each of the slave equipments 200-1-200-n is provided with a reception discrimination means discriminating whether or not a relevant slave equipment receives normally multiple address communication data to be received and with a notice data transmission means sending notice data to inform of it when part or all of the multiple address communication data are not normally received through the discrimination, and the master equipment 200 is provided with a multiple address communication transmission means sending multiple address communication data to all object slave equipments in a receptible way, a notice data reception discrimination means discriminating whether or not the notice data are sent after the transmission and a processing means conducting error processing corresponding to the transmission of notice data.