Cloud computing is provided on demand service via the internet, allowing users to pay for the service they actually use. Since cloud computing is emerging stage in industry, many companies and government consider adopting the cloud computing. Actually a variety of factors may influence on the adopting decision making of cloud computing. The objective of this study is to explore the significant factors affecting the adoption decision of enterprise cloud computing. A research model has been suggested based on TOE framework and outsourcing decision framework. Based on 302 data collected from managers in various industries, the major findings are following. First, the benefit factors of cloud computing service such as agility and cost reduction have direct and positive effects on adoption of the service. Second, lock-in as a risk factor of cloud computing service has a negative effect while security has not. Third, both internal and external environment factors have positive effects on adoption of the service.