A visual simulator has been developed as an example of Web-based education tool, which is written in Java Language, downloadable from web server and executable oil Web browser of Personal Computer It is necessary for beginners of Information Science to understand the internal structure and behavior of computers. Our simulator provides the following facilities: illustrating computer's internal structure graphically, interpreting sample assembly programs, demonstrating data transfer between registers of CPU and memory, and visualizing computer's detail behavior (von Neumann's style). This paper describes design concept of our simulator, its system configuration, instruction set and program to be interpreted by simulator and an effectiveness for both of education tool of classroom lecture and self-learning software after school.