Please look at the list of the countries that have the visa exemption agreement with Japan. If your country is included in the list, you usually do not need to apply for an entry visa to Japan.
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.
Read carefully the Japanese visa guide provided by the ministry of foreign affairs. For entry into Japan, a VISA may be required for attendees from some countries. Please make sure whether you need to apply for a VISA or not by contacting the local Japanese consulate or embassy in your country or visiting the website of Ministry of Foreign Affairs of Japan at http://www.mofa.go.jp/j_info/visit/visa/index.html
Know more about Japan Visa here: https://www.mofa.go.jp/j_info/visit/visa/index.html
*Please be kindly noted that The invitation letter from the organizing committee will be sent upon the request only when you register successfully, which may help but cannot guarantee you a Visa.
Should your application be denied, the conference organizing committee cannot change the decision of the Ministry of Foreign Affairs, nor will the organizing committee engage in discussion or correspondence with the consulate or the visa center on behalf of the applicant.