Foreigners wishing to enter Japan are required to apply at an overseas Japanese diplomatic establishment (embassy or consulate) for a visa that must be stamped in or attached to their passport, valid for travel to Japan. If they fail to obtain the appropriate type of visa, they might be denied entry into the country.
Therefore it is necessary to start the procedure to obtain an appropriate type of visa of your purpose of stay. The Certificate of Eligibility for Status of Residence which is issued by the Japanese Immigration Bureau is required for the visa application. It is advised to start this procedure 2 months prior to your expected arrival date to Japan. If you begin any later, you might not be able to obtain your visa in time, and it will be difficult for you to come to Japan as planned.