Critical thinking is an ability required for making proper judgments on things or problems in daily life, work or academic study. In this meaning, the ability should be learned in school education. The critical thinking ability consists of not only the knowledge and skills such as logical thinking, but also the attitude to apply these skills. Therefore, the critical thinking education requires a way for fostering critical thinking attitude. Debate in education has been regarded as an effective way of training the thinking skills, and is also expected to be effective for fostering the critical thinking attitude. In this study, a curriculum for fostering critical thinking attitude of high school students has been proposed, which includes a computer-based educational debate system. The proposed curriculum was applied to 438 high school students and evaluated its effectiveness by questionnaire surveys. The results showed that the proposed curriculum was effective for fostering critical thinking attitude. However, inquiring mind which is a component of critical thinking attitude only showed weak improvement.