These grapes are in season now. They are called "Delaware". According to something I read on the internet, they originally came from Delaware, Ohio. If you've ever tasted grape candy, that is what these taste like.
In Japan, the skins are usually quite bitter, so we don't eat them. Just pop them in our mouths and spit out the skins.
This bunch was about 6 inches long and 298 yen (about US$3). It may seem kind of pricey, but that is the usual cost for these. They are sweet and delicious.