This study aims to identify the mechanisms through which headquarters control their subsidiaries and the factors influencing such control. Recent studies on the headquarters-subsidiary (business unit) relationship in diversified or multinational corporations, based on the differentiated fit perspective, assume that headquarters can exercise differentiated control over their subsidiaries. This study questions the validity of this differentiation perspective and, through an in-depth case study of a multinational corporation's headquarters and subsidiaries, analyzes and identifies the headquarters' subsidiary control methods, the extent of differentiation (or homogenization) of control across subsidiaries, and the influencing factors. The major findings are as follows. First, in addition to the previously discussed performance control, behavior control, and cultural control, strategy control was confirmed as a major control mechanism employed by headquarters. Second, the headquarters' control approach was found to control two subsidiaries—which were contrasting in terms of competitive strategy, strategic mission, local environment, and capabilities—in nearly identical ways. This result completely contradicts the assumptions of existing subsidiary-level studies that presuppose differentiation. Third, headquarters were unable to differentiate their control according to subsidiary characteristics due to factors such as the headquarters' dominant logic, tight internal configurations among the components of the subsidiary control system, the non-discriminating nature (pervasiveness) of subsidiary control mechanisms, the headquarters' management capabilities and inertia, identical control structures and communication channels for subsidiaries, and the pressure for fair and equal control over subsidiaries. The main contributions of this study include providing a comprehensive and detailed description, classification, and analysis of headquarters' subsidiary control mechanisms through in-depth case research, and establishing a foundation for the development of new variables, theory building, and future research by identifying various factors influencing the headquarters' homogeneous control approach.