In order to improve the quality of embedded software, this paper proposes an enhancement to the ESIM (Embedded Systems Improving Method) by combining an IFD (Information Flow Diagram) with an Analysis Matrix to analyze unexpected obstacles in the software. These obstacles are difficult to predict in the software specification. Recently, embedded systems have become larger and more complicated. Theoretically therefore, the development cycle of these systems should be longer. On the contrary, in practice the cycle has been shortened. This trend in industry has resulted in the oversight of unexpected obstacles, and consequently affected the quality of embedded software. In order to prevent the oversight of unexpected obstacles, we have already proposed two methods for requirements analysis: the ESIM using an Analysis Matrix and a method that uses an IFD. In order to improve the efficiency of unexpected obstacle analysis at reasonable cost, we now enhance the ESIM by combining an IFD with an Analysis Matrix. The enhancement is studied from the following three viewpoints. First, a conceptual model comprising both the Analysis Matrix and IFD is defined. Then, a requirements analysis procedure is proposed, that uses both the Analysis Matrix and IFD, and assigns each specific role to either an expert or non-expert engineer. Finally, to confirm the effectiveness of this enhancement, we carry out a description experiment using an IFD.