An integrated software system has been under development which aims at analyzing and evaluating the effectiveness of man-machine system design from the viewpoints of various human factors, by simulating plant, man-machine interface and operator. In this paper, the configuration of this software system which is named SEAMAID is first introduced, followed by an explanation of how the operator simulator model is constructed. Also presented is an example of the operator simulator using Petri net model. We developed a prototype of the SEAMAID system, and the possibility of constructing a total system was confirmed by a simulation using prototype system. A model of human error analysis is also described.