This paper presents a comtmtational model of incremental utterance production in task-oriented dialogues. This model incrementally produces utterantes to propose the solution of a given problem, while simultaneously solving the problem in a stepwise manner. Even when the solution has been partially determined, this model starts utterances to satisfy time constraints where pauses in mid-utterance must not exceed a certain length. The results of an analysis of discourse structure in a dialogue corpus are presented and the fine structure of discourse that contributes to the incremental strategy of utterance production is described. This model utilizes such a discourse structure to incrementally produce utterances constituting a discourse. Pragmatic constraints are exploited to guarantee the relevance of discourses, which are evaluated by an utterance simulation experiment.