When introducing an information system such as an ERP system, consistency between business processes and IT systems is important. It is necessary to introduce the system after considering the business process (core competence) that will be a competitive advantage, such as site improvement and special customer service like Japanese manufacturing companies, and the standard functions of the ERP package system. In this study, conducted an exploratory case study of two ERP system introduction projects of Japanese manufacturing companies. As a result of the case study, it was found that the performance of the ERP system introduction was negatively affected if the introduction based on the core competence was not performed at the time of the ERP system introduction. Presented future analysis perspectives on the factors of user companies and SI vendor companies that have these effects.