In this paper, the authors report the effect of using FTAid and it has difference by education for making FT diagram. FTA is a method of analyzing and visualizing the causes of a fault event by Fault Tree diagram (FT diagram) in problem resolution of product and design processes. However FTA has a problem that is so many working hours to make a FT diagram without any misunderstandings and oversight. To solve this problem, the collaborative research group ; Jatco Ltd, The University of Tokyo and AIST, developed computerized support system named "FTAid". We distributed the FTAid to designers in JATCO, and analyzed FT diagrams made with FTAid and their working hours. We distributed the FTAid to designers in JATCO, and analyzed FT diagrams made with FTAid and working hours. As a result, the effect of using FTAid has difference by education for making FT diagram. Then we suggest FTAid needs education for making FT diagram to use it effectively.