The main purpose of this study was to develop a computer automated tool for fault tree analysis (FTA) in order to minimize the flaws of manual FTA. The automated FTA system developed in this study consists of two steps: 1) automatic fault tree conversion from a digraph, and 2) calculation of the probability of the occurrence of the top event and finding a minimal cut set of the top event. For the first step, we propose a new algorithm for automatic conversion of a digraph to a fault tree. The new digraph-FT conversion algorithm has eight FT generation rules to transform node information that is based on the node characteristics. Failures and faults are classified into three types to easily synthesize fault trees and analyze fault trees precisely. The automatic FTA system was then applied the analysis of real chemical processes to illustrate the effectiveness of the system.