We have developed an XML information retrieval system which can process queries by keywords or queries by combination of keywords and structural conditions. Queries by keywords are simple yet useful because users are not required to understand XML query languages or XML schema. While issuing queries by combination of keywords and structural conditions requires users to understand query languages and the underlying XML schema, we can restrict the target document fragments and the search conditions using structures in XML. The system was implemented on top of a relational XML database system developed by our group. The system can process both types of queries under a common relational schema. By carefully designing the database schema, the system handles a huge number of document fragments efficiently. For queries by keywords, we have developed a user-friendly interface for displaying search results. Our experiments using INEX test collection show that the system achieved relatively high precision and can process keyword set queries in acceptable search time.