1. An automatic answering device configured to answer automatically to a user utterance, the automatic answering device comprising: an input unit configured to accept a user utterance; and an output unit configured to output a reply sentence in a form recognizable by a user, in response to the user utterance accepted by the input unit, wherein the reply sentence is determined based on a conversation scenario which is a set of inputted sentences and reply sentences, the inputted sentences each corresponding to a user utterance assumed to be uttered by the user, the reply sentences each being a reply from the automatic answering device to the inputted sentence, and data of the conversation scenario have a data structure that enables the inputted sentences and the reply sentences to be expressed in a state transition diagram in which each of the inputted sentences is defined as a morphism and the reply sentence corresponding to the inputted sentence is defined as an object.
2. The automatic answering device according to claim 1 , wherein the conversation scenario includes a scenario which describes, as a single morphism, an inputted sentence corresponding to all the user utterances other than a user utterance containing a predetermined content, and any of inputted sentences corresponding to all the user utterances are linked with any one of the reply sentences in the scenario.