1. A fault diagnosis method for diagnosing an apparatus comprising a plurality of sensor nodes and a plurality of part nodes which are directly or indirectly associated with said plurality of sensor nodes, comprising the steps of: a) before fault diagnosis, a1) setting linkages based on deliveries of signals among said plurality of sensor nodes and said plurality of part nodes, and establishing weighing factors indicating correlations between said plurality of sensor nodes and said plurality of part nodes forming the linkages; a2) classifying said plurality of sensor nodes and said plurality of part nodes into a plurality of subsystems; b) during fault diagnosis: b1) collecting output signals of said plurality of sensor nodes; b2) converting the collected output signals of the plurality of sensor nodes to state quantities indicating degree of abnormal operation of the plurality of sensor nodes; b3) calculating state quantities indicating an abnormal operation of respective part nodes having a linkage with respective sensor nodes; b4) consolidating the state quantities for the plurality of sensor nodes and the plurality of part nodes obtained at steps b2 and b3 for each of said plurality of subsystems; and b5) performing fault diagnosis on said plurality of sensor nodes and the plurality of part nodes on the basis of the consolidated results of step b4, wherein a state quantity value is used as a basis for fault diagnosis.