A requirements analysis step plays a significant role on the development of information systems, and in this step we produce various kinds of abstract models of the systems (called requirements models) according to the adopted development processes, eg class diagrams in the case of adopting object-oriented development. However, constructing these models of sufficient quality requires highest intellectual tasks and skills of human requirements analysts. In this paper, we develop a computerized tool to extract from a set of Japanese text documents conceptual information, called conceptual graph, which can be used as intermediate representation to generate software requirements models. More concretely, by applying the variation of text-mining techniques that we have developed, we extract significant words from text documents referring to the same problem domain and identify relevant relationships among them. The extracted words can be considered as concepts and they are constituents of a conceptual graph in the domain. This constructed graph can be used for generating requirements models, eg object oriented models, feature model, and even as a domain ontology that can be utilized during requirements analysis activities. We have made experimental analyses of our tool. This paper also includes the discussion on how the extracted conceptual graph can act as an object-oriented model, a feature model and a domain ontology, in order to show its wide applicability.