A failure diagnosis apparatus for diagnosing a failure in a vehicular electronic control system includes a plurality of electronic control related members mounted on a vehicle, a multiple communication line connected to the plurality of electronic control related members as communication elements, such that communication signal information received from the multiple communication line is analyzed by an analyzing portion. A communication system region which may have failed in the multiple communication system is specified based on presence or absence of communication of the electronic control related members, and the electronic control related member which may have failed is specified based on a data content of a communication signal provided from communication information. Respective states are displayed by proper value data and detected value data of the electronic control related members.