E-mail : isd@office.chiba-u.jp
Re-entry permission is permission which is granted prior to departure by the Minister of Justice in order to simplify the immigration (entry and landing) procedures in cases where foreign nationals residing in Japan temporarily depart from Japan and intend to re-enter Japan.
If you re-enter Japan within one year (or by the expiration date of the status of residence) after leaving Japan provisionally, and continue the same activity in Japan, "special re-entry permit" is applied.
If the period of your authorized stay is more than one year, and you will leave then re-enter Japan more than one year later to continue the same activity, you must obtain a "Re-entry Permit" before you leave Japan.
Before temporarily leaving Japan, notify the administrative office of your faculty / graduate school.
International students in possession of a valid passport and resident card who will be reentering Japan within one year of departure to continue their activities in Japan, in principle, will not require a re-entry permit(this is called a special re-entry permit).
However, if your period of stay expires within one year of temporarily leaving Japan, please make sure to re-enter Japan before the expiration of your period of stay.
Please make sure to tick the correct box on the Embarkation and Disembarkation Card for Re-entrants if using this free system.
https://www.isa.go.jp/en/applications/procedures/16-5.html
http://www.moj.go.jp/isa/content/930002122.pdf
When the period of stay remains more than one year before the expiration date, and you re-enter Japan after more than one year and continue the same activity, you do not have to obtain a new visa as long as you have obtained re-entry permit before leaving Japan.
There are single re-entry and multiple re-entry permission. The validity period of re-entry permit is limited to within a current date of expiration. Please apply for a re-entry permit at the regional immigration bureau.
If you leave Japan without “Special re-entry permission” or “Re-entry permission”, you are considered to have relinquished the status of residence that you hold at that time. In this case, you must obtain a new visa before returning to Japan. It may take a considerable period of time to obtain a new visa. In the case of a temporary departure from Japan while enrolled or research at the university, please be sure to obtain “Special re-entry permission” or “Re-entry permission” before leaving Japan.