In a system where resources are used in a varying manner, when performances are monitored based on detected past behavior when the system was operating normally, if performance behavior is detected that is different, it is difficult to determine whether the detected performance behavior results from resources being used differently than when the system was operating normally. According to the present invention, monitoring accuracy is improved by determining whether performance behavior results from change in characteristics relating to the usage of the system by using means for measuring performances when the system is in operation and detecting a performance different from when the system was operating normally, means for measuring characteristics relating to the usage of the system and detecting whether the characteristics are different from when the system was operating normally, and means for comparing performance information with characteristic information relating to the usage of the system.