1. An operation management apparatus, implemented using a processor and a memory, which monitors performance information of a system executing a service and extracts correlation variants of the performance information so as to allow a management to detect and localize a performance-degrading fault of the system, said operation management apparatus comprising: a normal model range accumulation unit, implemented using the memory, that accumulates a normal range of correlation collapse measured in a normal operation of the system; a fault model range accumulation unit, implemented using the memory, that accumulates a fault range of correlation collapse measured in a faulty operation of the system; a correlation variant range discrimination unit, implemented using the processor, that determines whether or not a range of correlation collapse ascribed to the performance information falls within the normal range of correlation collapse; a correlation variant history accumulation unit, implemented using the memory, that accumulates a history regarding the range of correlation collapse ascribed to the performance information which does not fall within the normal range of correlation collapse; and a fault model discrimination unit, implemented using the processor, that determines whether or not the history accumulating a predetermined number of ranges of correlation collapse approximates to the fault range of correlation collapse, thus discriminating a fault model on the basis of the performance information.