Interests on Service Level Agreement(SLA), an immanence operating tool for managing the level of the information system service objectively and qualitatively, were raised among IT outsourcing service providers, outsourcers, and operating departments. Yet, only a few domestic conglomerates adopted the SLA, and exact usage of the SLA is currently unknown. Because of the importance of the SLA between a service recipient and a service provider, the agreement is treated with high confidentiality. This raised the problems to organizations which are considering the SLA but lack in the concrete guide line to internalize SLA management process. This study provides the process model of implementation for SLA by conducting multiple case research. The sampled companies are currently implementing the SLA over 1 year of usage period. Factors were used to provide the managerial contribution for implementing the SLA. To analyse the case samples, in-depth interview method was conducted for each sampled company. As a result, if SLA can be used as an immanence managerial tool and can be actively implemented, it will be an strategic tool for various decision making in IT management practice with long term relationship, better shared partnership, and continuous service improvement.