"Yonahanmachi" is the name of a fictionalized place in Japanese manga artist Gosho Aoyama's work "Detective Conan", where Conan lives and studies. In the work, Detective Mori's office, Tidan Elementary School, Tidan High School, and Nichibei Television are all located in Yonahamachi.

Because of the proximity, some people mistakenly confuse "Yonahanamachi" with "Kojimachi". In the original Detective Conan, there are many references to Yonahanmachi. The name is a fictionalized image of the streets of Ikebukuro, Shinjuku and Shibuya, not the real Kojimachi, and is not based on Kojimachi.