Document-searching using a compiling device for generating a two-state input automaton for enabling a state transition by storing an input query expression, performing parsing, and reading at least two states from different types of nodes in an element identifier, and a storage device for storing the two-state input automaton. Also included is an automaton-evaluating device for enabling three state transitions by reading out a two-state input automaton from the storage device and storing the automaton, while reading in a document and identifying the input two states.