1. An automaton determinization method comprising: state-generating that includes generating a second state newly, when there are two or more first transitions that leave from a first state included in a finite state automaton and that are assigned with a first symbol; first-transition-generating that includes generating a second transition that leaves from the first state and enters to the second state and that is assigned with the first symbol; second-transition-generating that includes generating, with respect to each of the first transitions, a fourth transition in which a state previous to a third transition is substituted with the second state, the third transition being an outgoing transition from next states of the first transition; and first-deleting that includes deleting states that are next states to the first transitions in which the fourth transitions are generated and that do not have incoming transitions other than the first transitions, deleting outgoing transitions from the deleted states, and deleting the first transitions in which the fourth transitions are generated.