A foreign national who, during his period of sojourn leaves Korea to return before the period of sojourn has expired, that foreign national must have a Re-Entry Permit . A foreigner who leaves Korea without having obtained a Re-Entry Permit will, while overseas, have to get a new entry visa and, after returning, go through the process of alien registration all over again if he intends to stay for 91 days or more.
A foreigner who enters Korea with a multiple visa may leave Korea and return a limitless number of times during his period of sojourn without needing an additional Re-Entry Permit.

There are two types of Re-Entry Permit; Multiple Re-Entry Permits , which allows one to leave and return numerous times, and Single Re-Entry Permits , which may only be used once.
Apply for Re-Entry Permits at the Immigration Office in your area. One may apply for a Re-Entry Permit at the airport Immigration Offices at Incheon and Gimhae, but you can only receive a Re-Entry Permit this way once

Documentation to Prepare

Passport and Alien Registration Card, approval or recommendation from head of training company in the case of Industrial Trainees, and fee of 30,0000won for Single Re-Entry, 50,000won for Multiple Re-Entry.