Fumotoppara is one the famous camping site in Japan. Located in Sizuoka prefecture, it is a dream place for every campers all around the year for every camping enthusiast.
I spend two days here. Place itself is quite spacious, but you need a reservation in advance to camp in this site. Check in and out is quite flexible, and fees per person is 2000 yen.
Check the local website for more info.
AloJapan.com