Please look at the list of 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.
For those who require a visa, please note that the Organizing Committee has no control over the visa application process, or the decision of the visa adjudicator in the embassy or consulate. The conference cannot be responsible for actual visa issuances. The process length varies from individuals, you’re strongly advised to start your application as soon as you can.