I want to check if the road is a public road.

We can confirm in authorized route map of road ledger figure information "Yokohama no Michi" in "administrative map information" of Motoichi homepage. In addition, we can read authorized route map in [city hall the second floor "Yokohama Building Information Center"] or [Public Works Office of each ward].
※Contact 22nd floor of 10 City Hall, 6-50 Honcho, Naka-ku [Road and Highway Bureau Road Investigation Division] (TEL045-671-2774)

<Related Homepage>
Road ledger map information "Yokohama no Michi"
http://wwwm.city.yokohama.lg.jp/ (outside site)

Answer:
Road Investigation Division
Phone: 045-671-2774 FAX: 045-550-4954