Recently, congress amended the Act on External Audit of Stock Companies to improve accounting transparency and reliability in firms. In particular, mandatory auditor designation have been greatly expanded through this revision. Therefore, this study systematically summarized and discussed the mandatory auditor designation regulation. First as a result of the audit review of the FSS within the past six years, firms with no accounting standard violations are excluded from the periodic designation. However, the theme audit review of FFS does not audit review on financial statements but an audit review on specific accounting issues. Therefore, the theme audit review firms should be included in the periodic designation. Second, to promote the KONEX, pre-IPO firms were excluded from designation of auditor. Also, since financial institutions are supervised by the FSS, they were excluded from designation of auditor. However, to protect outside investors, firms that are pre-IPO on the KOSPI and KOSDAQ are designated auditor. In addition, the FSS oversees the soundness of operations for financial institutions, but FSS does not oversee the accounting for financial institutions. Thus, it is necessary to exclude the auditor designation exception for these reasons. Third, due to the introduction of the auditor registration system, many small accounting firms are expected to make changes such as organizational changes and mergers to meet the registration requirements. However, it is not known whether audit quality will improve in this environment. Therefore, considering the quality control level of the accounting firms, it is necessary to implement the auditor registration system step by step. Also, the policy to improve audit quality of medium and large accounting firms is missing from amendment of the External Auditing Law.