In order to apply for double entry visa you must have visited South Korea at least once before
In order to apply for multiple entry visa you must have visited South Korea at least 4 times before
Double-Entry / Multiple-Entry Visa Condition for Business Visa Applicants:
2. 1 time prior visit (double);
4 time prior visit (multiple);
3. NOC should explain the need for double OR multiple entry;
4. Invitation Letter should explain the reason for multiple entry request;
5. Guarantee Letter must cover the whole period of the visa validity (ex: 1 year for multiple entry).