A new method of document layout analysis is proposed for a document reader to be used for reading a wide variety of documents. Emergent computation, which is a key concept of artificial life, is adopted to analyze various complex document structures. The proposed method uses a multi-layer architecture consisting of four subsystems: region extraction, region analysis, region recognition, and region modification. Emergent computation is used for the interactions between subsystems to produce effective and flexible behavior of the entire system. The global layout structure of a document is extracted from these interactions. Experimental results obtained for 150 documents show the method is adaptable to various layout structures in documents.