An electronic control network system for an electric vehicle , comprising: a plurality of electronic control units which control a behavior of electronic devices; and a network which connects the electronic control units to each other, wherein: any two or more of the electronic control units are configured as synchronization execution nodes which exchange communication frames including time synchronous information to thereby establish time synchronous communication, and the remaining electronic control units are configured to perform time synchronous communication in accordance with the established time synchronous communication; and wherein the electronic control units are classified in two groups, of which the first group comprises electronic control units , which affect running of the electric vehicle , in case one or more break down, and of which the second group comprises electronic control units , which do not affect running of the electric vehicle , in case one or more break down; and the synchronization execution nodes are selected from the electronic control units of the first group, wherein at least one electronic control unit of the first group performs electronic control on power of the electric vehicle , which disable the behavior of the electronic device if one or more of the synchronization execution nodes break down. a plurality of electronic control units which control a behavior of electronic devices; and a network which connects the electronic control units to each other, wherein: any two or more of the electronic control units are configured as synchronization execution nodes which exchange communication frames including time synchronous information to thereby establish time synchronous communication, and the remaining electronic control units are configured to perform time synchronous communication in accordance with the established time synchronous communication; and wherein the electronic control units are classified in two groups, of which the first group comprises electronic control units , which affect running of the electric vehicle , in case one or more break down, and of which the second group comprises electronic control units , which do not affect running of the electric vehicle , in case one or more break down; and the synchronization execution nodes are selected from the electronic control units of the first group, wherein at least one electronic control unit of the first group performs electronic control on power of the electric vehicle , which disable the behavior of the electronic device if one or more of the synchronization execution nodes break down. any two or more of the electronic control units are configured as synchronization execution nodes which exchange communication frames including time synchronous information to thereby establish time synchronous communication, and the remaining electronic control units are configured to perform time synchronous communication in accordance with the established time synchronous communication; and wherein the electronic control units are classified in two groups, of which the first group comprises electronic control units , which affect running of the electric vehicle , in case one or more break down, and of which the second group comprises electronic control units , which do not affect running of the electric vehicle , in case one or more break down; and the synchronization execution nodes are selected from the electronic control units of the first group, wherein at least one electronic control unit of the first group performs electronic control on power of the electric vehicle , which disable the behavior of the electronic device if one or more of the synchronization execution nodes break down. <EOS>