The current study examines the dialect of Okayama city, particularly the sentence-final particle de, which is analogous to the Japanese common language sentence-final particle yo. A comparison of de and yo revealed two main findings. First, similar to the Japanese common language, the basic meaning of de in the Okayama city dialect is to display mental manipulation and represent a gap in recognition. The particle de conveys different meanings based on its intonation: pronouncing de with a rising intonation indicates the compulsion of mental operation, while a falling tone indicates the delegation of mental operation. Second, in the Okayama city dialect, de can be used in different ways. It can be used to express something that is not apparent to the speaker or to refer to the display of a limited gap in recognition, and it does not require a reaction from the audience.