Japan’s rail services are one of the best in the world. They are extremely efficient and go just about everywhere in Japan. If you plan to do a lot of travelling in Japan then you should consider the Japan Rail Pass. The pass allows for unlimited travel on the national JR network, including the shinkansen (bullet trains) excluding the Nozomi superexpress.
This pass can only be purchased outside of Japan and will save you travel money in Japan.
If you plan, like most tourists to travel the Golden Route of Tokyo – Kyoto – Osaka – Hiroshima it is well worth looking at this pass. You must be travelling in Japan under the visa status of “temporary visitor” to be eligible.