1. A speech processing system, comprising: utterance input means for receiving an input of utterance information including a speech signal representing an utterance and prescribed environmental information representing an environment in which the utterance is made; speech recognition means for performing speech recognition on the speech signal in the utterance information received by said utterance input means and for outputting a recognition result as a text; data processing means for executing a prescribed data processing on the text output by said speech recognition means; utterance sequence model storage means for storing an utterance sequence model statistically trained such that upon reception of a text of an utterance and said prescribed environmental information, a probability of an utterance in a prescribed set of utterances to be uttered successively following the utterance represented by said text can be calculated; utterance storage means for storing utterances in said prescribed set of utterances and degree of confidence of data processing when each of said utterances in said set of utterances is processed by said data processing means; and utterance candidate recommendation means, for scoring, in said set of utterances, candidates of utterances to be recommended to a user who made the utterance recognized by said speech recognition means, based on an evaluation score obtained by combining, in a prescribed form, a probability calculated for each utterance in said prescribed set by said utterance sequence model stored in said utterance sequence model storage means, using the result of recognition by said speech recognition means of the utterance information received by said utterance input means and the environmental information included in the speech information, and the degree of confidence of said data processing on each utterance in said prescribed set of utterances, and for recommending an utterance candidate to the user based on the scores.