Incheon international airport has been successful, that is, the winner of Airport Service Quality (ASQ) evaluation performed by ACI(Airport Council International) for nine consecutive years. It goes without saying that such an outstanding performance was made not only by airport authority itself but by the collaboration among subcontractors at Incheon international airport. Since Incheon airport is showing more than 80% of outsourcing rate, it is important to mention and study the roles and functions of subcontractors who has made a major contribution to ASQ performance. According to empirical research in this paper, it was found out service attitude, communication skill and interdependence between airport authority and subcontractors were important factors affecting the ASQ score. It is also analyzed that those independent factors have an impact on ASQ performance through the intermediate factor of trust. As a result, service attitude and interdependence between airport authority and subcontractors have statistically a significant effect to the relational satisfaction and ASQ performance. It could be concluded that trust is significant factor determining the causal relationship among service attitude, communication skill, relational satisfaction and ASQ score.