A structured-document management apparatus includes data storage which stores a plurality of structured document data items each including a plurality of elements, common-structure storage which stores a common structure including a plurality of structures included in the structured document data items, a first acquisition unit configured to acquire a new structured document data item, an update unit configured to update the common structure into a new common structure including the structures and a plurality of structures included in the new structured document data item, a second acquisition unit configured to acquire a differential structure between the new common structure and a structure of the new structured document data item, differential structure storage which stores the differential structure, and a storing unit configured to store an array of elements of the new structured document data item into the data storage, the array being arranged based on the differential structure.