Gujo-hachiman is in Gifu, which is a prefecture in Japan.
The following two figures explain where is Gujo-hachiman.
The first figure shows the location of Gifu prefecture in Japan. Gifu prefecture is located in almost the center of main islands of Japan. The capital of Gifu prefecture is Gifu city. Gifu city is about 390km apart from Tokyo, about 40km apart from Nagoya, and about 180km apart from Osaka.
The second figure shows the location of Gujo-hachiman in Gifu prefecture.
You can see that Gujo-hachiman is located in almost the center of Gifu prefecture. So you can recognize that Gujo-hachiman is almost the center of the main Island of Japan :-).
Gujo-hachiman town is about 50km apart from Gifu city, the capital of Gifu prefecture.