Apparatus and method for generating a summary according to hierarchical structure of topic

A text summarizer detects the hierarchical structure of topics in a document and extracts boundary sentences corresponding to the turning point of a topic from a candidate section of a topic boundary using the relation degree between a sentence and a topic passage. Then, the text summarizer extracts topic introductory sentences serving the purpose of introducing a topic from the introductory part of the topic beginning with this boundary sentence, and generates a summary using both the boundary sentences and topic introductory sentences.