A Jin Air Boeing 777-200, registration HL7733 performing LJ-4 from Bangkok (Thailand) to Seoul (South Korea) with 392 passengers and 10 crew, was preparing for departure, the APU was running, when suddenly smoke entered the aircraft. The passengers disembarked rapidly. 4 people needed treatment for smoke inhalation. The airline reported the APU was identified as source of the smoke, the APU was replaced. The occurrence aircraft was able to depart and reached Seoul with a delay of 7 hours.