To improve the processing speed of a morphological analysis system, an analysis processing part retrieves words constituting a natural language sentence from a word dictionary, retrieves concatenation rules from a grammar dictionary, creates an automaton based on the words and the concatenation rules, and obtains a morphological analysis. The grammar dictionary stores rules integrating concatenation rules representing non-null transitions and concatenation rules representing null transitions in which transition sources of the first concatenation rule are their transition destinations. To create the automaton, an optimal solution searching part of the analysis processing part generates, responsive to an input word entered into the automaton, states necessary for transition according to the concatenation rules corresponding to the input word without generating any state that can be transited by pursuing a null transition succeeding the generated states.