This paper proposes a conversational style text-to-speech synthesis scheme based on an analysis of fundamental frequency, F0. Through the analysis, we confirm that conversational F0 can be represented by the superpositional model using three components ranging utterance, major phrase, and minor phrase. We compare each component of the model between conversational style and reading style to investigate the following points: where big F0 discrepancies are found, what linguistic factors concern to the discrepancies, and to what extent do such discrepancies occur. This paper uses real domain data that includes a lot of linguistic context. Analysis confirms that large differences occur in global components such as single span whole utterances and phrases, and that the differences occur at or around domain-specific expressions. The analysis also reveals that local components are almost the same in both styles. These analyses show that it is necessary to estimate the utterance and phrase components from words attributes other than the grammatical clues to realize conversational synthesis in the super positional manner.