This study clarified the relationship between the three companies, including the subsidiary, which has been maintained for many years, with respect to how trust is central to the intercompany relationship and what effects appear between the companies. This paper revealed the following three things. for (1) in Discussion 1, both companies had explained the situation to their subordinates and others around them, so they had fulfilled their roles. For (2), they were quite familiar with each other's organizational characteristics, as we understood from the interviews. For (3), they were fulfilling their accountability to their own organization to their superiors, and at the same time, they were explaining to their subordinates, so their negotiation behavior was properly conducted. The organizational set perspective of the case between the three companies in this study allowed us to clarify the respective roles of Company A, Company B, and Company C. As a result, it was inferred that the alliance would be stronger and deeper when the third company's organization intervened in the inter-organizational relationship theory. The relationship among the three companies, from a long-term perspective, led to the expansion of new sales channels as open products added high value and were sent to overseas sales networks. In addition, diversity in products has been created, leading to supply chain management functions, communication of needs in the field, and improvement of information networks and products, thus having a competitive advantage. It was confirmed that the basis for this is the formation of "trust," in which the role of the person in charge of the border is well done. It was confirmed that the assumptions of the resource dependence perspective are being flexibly addressed. We also discussed how the process of trust between organizations goes through the stages of alliance development and evolution. The results suggest that an important factor in the maturation of an alliance is to go through a process in which trust is asymmetrical before the alliance reaches maturity. However, this insight is based on a single case study, and the sample size for qualitative research is insufficient. In addition, this study focused on inter - organizational relationships within Ishikawa Prefecture. Therefore, it is necessary to deepen the discussion based on other regional characteristics. We would also like to clarify in future research whether universality can be found in supply chains with other affiliations.