This study examines the process of poor governance and ineffective internal accounting management system(IAMS) stemming from low-level management ethics, which affects the motivation, opportunities, and rationalization of embezzlers. The improvement and strengthening of the IAMS has attracted media and industry attention as the main focus of the amended External Audit Act, along with the standard audit time system and the periodic designated audit system. Despite the growing interest in the IAMS, the embezzlement incident at Osstem Implant can be seen as a representative example of the poor operation of the IAMS of domestic companies. According to the fraud triangle theory, corporate fraud occurs when the three axes of motivation, opportunity, and rationalization are established at the same time. The embezzlement case of Osstem Implant is based on the social and economic background of overheating in the stock market, which is believed to have affected the motivation and rationalization of fraud. The IAMS plays a role in suppressing opportunities among the three elements of injustice, and the ethical consciousness of management, the subject of organizing and operating it, has a key impact on the composition and operation of the IAMS. Prior to the incident, owner risks have been raised for the company, and problems have been found in the overall governance structure. For instance, the low ratio of outside directors, the composition of outside directors excluding financial experts, and their low board meeting attendance and poor treatment for them. Along with it, the rapid reduction of the internal control staff is believed to have provided the embezzler with the opportunity by leading to the IAMS failure. The high level of real earnings management of the company and the company's low governance score suggest that preemptive actions were needed. In addition, accounting firms, financial institutions, and government authorities, which are external stakeholders of Osstem Implants, are also evaluated to have failed to properly perform their respective roles. The incident at the company suggests the need to supplement and check the role of domestic companies and external stakeholders in the internal accounting management system.