Please refer to the list of the countries that have the visa exemption agreement with Japan. If your country is included in the list, you will not be required for a visa when entering Japan under normal circumstances.
If your country is not included in the list, you need to obtain a short-term stay visa (“tanki-shouyou visa” in Japanese) from the embassy of Japan in your country.
Please read the Japanese visa guide provided by the ministry of foreign affairs carefully and be informed that it is the embassy of Japan in your country that makes a decision on issuing a visa.
Usually the procedure takes considerably long, so you need to begin the procedure as early as possible.
If you need to submit invitation letter and more information by organizer, please contact to local secretariat : firstname.lastname@example.org