We have implemented a Japanese text processing system, combining the existing parser and dictionary with the linguistic resources that we developed based on systemic functional linguistics. In this paper, we explain the text understanding algorithm of our system that utilizes the various linguistic resources in the Semiotic Base suggested by Halliday. First, we describe the structure of the SB and the linguistic resources stored in it. Then, we depict the text understanding algorithm using the SB. The process starts with morphological and dependency analyses by the non-SFL-based existing parser, followed by looking up the dictionary to enrich the input for SFL-based analysis. After mapping the pre-processing results onto systemic features, the path identification of selected features and unification based on O'Donnell are conducted with reference to the linguistic resource represented in the system networks. Consequently, we obtain graphological, lexicogrammatical, semantic and conceptual annotations of a given text.