In recent years, the open innovation which utilizes the external resources broadly in a field of research, technology and product development is getting a lot of attention both academically and managerially. But, from a viewpoint of traditional differentiation strategy, an excessive dependence to the external resources is said not to contribute the firm's competitive advantage. This paper discusses the role of the information systems achieved to practice of the open innovation in the core business in Japanese firms. Therefore, we performed preliminary analysis using our original questionnaire survey data carried out in 2007 targeting manufacturing firms in Japan. As a result, we elucidated that insourcing or quasi-outsourcing is not necessarily preferred even if it is a case so that information systems may carry out an indispensable and/or important contribution to operate a core business. However, we also showed clearly that a firm positively makes an effort toward to maintain and/or improve the knowledge and skills about information systems operation in that case.