In technical documents, diagrams are generally utilized with expository text aiming at concise presentation of information. Since the information is conveyed by both text and diagrams, it is necessary to understand both of them to extract information from documents. In this paper, we propose a method of understanding of expository text with diagrams. One of the central issues of such understanding is how to cope with ambiguities in the results of processing of text and diagrams. To solve this problem, the following steps are employed: (1) Information extracted from text and a diagram is described based on the common representation called relational representation which enables us to describe the ambiguities explicitly. (2) The extracted relational representations are unified by hypothesizing the references from text to a diagram. (3) The niari.murn and consistent set of hypothesized references is obtained to resolve ambiguities. Based on the experimental results for some pairs of text and a diagram, we discuss the advantages and the limitations of our method.