1. A method for speech recognition comprising: a feature-amount extracting step for extracting a feature amount based on a frame of an input utterance; a storing step for determining whether a current processing frame is within or at an end of a candidate word previously registered, and storing the candidate word on the basis of a first hypothesis-storage determining criterion when within a word and on the basis of a second hypothesis-storage determining criterion when at a word end; a developing step for developing a hypothesis by extending utterance segments expressing the word when a stored candidate word is within a word and by joining a word to follow according to an inter-word connection rule when at a word end; an operating step of computing a similarity of between the feature amount extracted from the input utterance and a frame-based feature amount of an acoustic model of the developed hypothesis, and calculating a new recognition score from the similarity and a recognition score of the hypothesis of up to an immediately preceding frame calculated from the similarity; and a step of repeating the storing step, the developing step and the operating step until the processing frame becomes a last frame of the input utterance, and outputting, as a recognition result approximate to the input utterance, at least one of hypotheses in the order of higher recognition score due to processing the last frame.