It is essential to quantitatively estimate the performance of fault diagnosis. In particular, two quantitative performance criteria are very important: diagnostic reliability and diagnostic accuracy. Each criteria is defined for the design phase and the running phase, respectively. This paper addresses diagnostic reliability for the running phase and diagnostic reliability and accuracy for the design phase. A fault diagnostic method utilizing signed directed graph is proposed. In this paper, a modified fault diagnosis method which has higher diagnostic accuracy. than the aforementioned method＇s diagnostic accuracy is proposed. The proposed method uses conditions for cause-effect relationship among state variables. Furthermore, the performance of the proposed method and criteria is demonstrated by use of mini-plant.