If you stay in Korea for more than 90days, you should have the ARC according to Immigration Act. It is evidence to prove that you have a right to stay in Korea within valid. If you have ARC, you do not need to bring your passport all the time.

• Those intending to stay in Korea for more than 90 days after entry
• A former Korean who have acquired a foreign nationality after losing the Korean one or a foreigner born in Korea, who are given residence status and intend to stay for more than 90 days.