1. A fault diagnosis method for specifically identifying a faulty component by using knowledge of fault diagnosis based on data expressing features or states of an objective under diagnosis, the method comprising the steps of: providing problem localizing knowledge for identifying a faulty component based on an operation principle of said objective under diagnosis, heuristic knowledge for localizing the faulty component based on available expertise, and meta-level diagnosis knowledge for determining a scheme of using said problem localizing knowledge and said heuristic knowledge; and, executing a reasoning for the faulty component of said objective under diagnosis through a combination of a reasoning based on the use of said problem localizing knowledge and a reasoning based on the use of said heuristic knowledge in accordance with said meta-level diagnosis knowledge by localizing the faulty component by omitting intermediate steps involved in the diagnosis which are determined in accordance with said heuristic knowledge based on data obtained during the diagnosis; determining applicability of said omitting; providing a stepwise execution mode in which a diagnosis processing is interrupted every time execution of one diagnosis step has been completed; providing a one-path execution mode in which the diagnosis processing is interrupted every time one faulty component has been identified; providing an all-path execution mode in which the diagnosis processing is terminated when all faulty components have been identified; providing flags for discriminatively indicating diagnosis steps executed in said one-path execution mode and diagnosis steps executed in said all-path execution mode in association with said problem localizing knowledge; detecting a flag indicating that a given diagnosis step to be executed has previously been executed from said flags upon identifying a faulty component either in said one-path execution mode or said all-path execution mode; and, aborting execution of said given diagnosis step while regarding the result of said execution as being unsuccessful when the detecting occurs.