A new mediator model for Information service firms (ISFs) is proposed based on Service dominant logic. In this model, mediators create a shared contextual place and it plays an important role in connecting and managing supply and demand to provide superior services. The mechanism of value co-creation based on service dominant logic in business activities through a suitable service field organized by mediator firms for interactions by all participants. This mechanism is demonstrated through case studies of the framework of Hitachi TWX-21 and Cookpad Inc., which are Japanese information service businesses. We found that a good service field was effective in helping all business’s parties receive better value and gain satisfaction.