This paper examines effects of risk compensating changes in behavior when an automated safety system is introduced and when the levels of the automation are varied. Two experiments were conducted using a microworld. The first experiment clarified the differences in the human's operation method and the operation risks among three control modes:(1) no aid is given to the human,(2) a warning signal appears when necessary, and (3) a warning signal appears and then the automation intervenes into control to prevent an accident. The results show significant risk compensatory changes in behavior when the safety system not only provides a warning, but also performs safety control actions, when necessary. It was also discovered that even if the automation system functions properly, new types of accidents arise, resulting in an equivalent number of accidents. The second experiment examined whether the change in behavior when the level of automation changes depends on the direction of the automation level shift. The results show that the risk reducing behavior change that occurs when the level of automation is decreased is not as significant as the risk compensatory change that occurs when the level of automation is increased.