In the field of automobile development, the recent automotive functional safety standard (ISO 26262) is now applicable. However, it is difficult to develop a system so as to comply with the standard. In this paper, I will focus on the concept phase of this standard because it includes the new ideas to keep a system safe. For example, the idea of "item" is one of them, and it means an abstraction of a system. It is important to think about safety in the very early phase because we can change the behaviour more readily than do after designing. On the other hand, it requires us to devise the new approach to calculating risk (a.k.a. ASIL) because we don’t have detailed information on an item in the early phase development. In this paper, we introduce our approach CARDION, and we show how we deal with those characteristics of the standard.