An object cooperative network system for executing processing in cooperation between objects connected by a common communication path. Each of the objects includes a transmitting section to transmit messages that include predetermined information to the network system. In addition, each object includes a monitoring section to monitor the predetermined information of the transmitted messages, and a reaction table to indicate correspondence between the transmitted messages. Each of the objects sets information to which the object should respond in the monitoring section, and receives a message to execute processing by making reference to the reaction table when information to which the object should respond is detected.