Many embedded systems not only affect their context through actuators but also are affected by the context through sensors. It is important to provide a context-dependent development method for constructing safe and reliable embedded systems. However, most of the current requirements analysis methods do not explicitly provide a systematic way for deciding the boundary of the context that should be taken into account because it is essentially difficult to decide which context element should be included as the targets of requirements analysis. If a developer explores the context boundary in an ad-hoc manner, he or she will be faced with the frame problem because there are unlimited context elements in the real world where the target system exists. To deal with this problem, this paper proposes a context-dependent requirements analysis method called CAMEmb (Context Analysis Method for Embedded systems) in which only the value-context elements are extracted as the associated context elements. Applying the guide words provided by CAMEmb, we can explore only a sequence of context elements directly or indirectly affecting the data value observed or controlled by the system sensors and actuators. Other context elements not affecting the system observation and control are not taken into account because these context elements do not affect the system behavior. Using CAMEmb and lightweight formal tools, we can explore the context boundary that guarantees the expected system behavior. We developed CAMEmbModeler, a support tool consisting of a CAMEmb-based modeling editor and a model compiler that transforms system and context models into the design model reflecting the context boundary.