This study examines the effect of the mandatory designation rule on audit fees charged and audit hours rendered by auditors for firms released from the mandatory auditor designation rule in the Korean audit market. Under the mandatory auditor designation rule, which took effect in 1991, problematic firms are assigned new auditors by the Financial Supervisory Service. Previous studies suggest that this regulation positively affects the quality of audits by promoting auditor independence. Thus, this study hypothesises that firms that have been subjected to mandatory auditor designation improve the quality of their financial reporting, and that auditors hired after the mandatory designation period account for reduced audit risks when determining audit fees and audit hours. This study shows that audit fees and audit hours of firms released from the mandatory auditor designation rule are lower than those of other initial audit engagements. Taken together, this study's findings reinforce the notion that auditors' perceptions of changes in audit risk yield corresponding changes in the audit fees they charge and audit hours they render.

Credible audit quality is a precondition for a firm’s sustainability. External auditors offer assurance with regard to the uncertain factors that can jeopardize a firm’s sustainability and provide audit opinions that help investors assess risk. After the global crisis and accounting scandals, mandatory audit firm rotation has been implemented globally. However, few studies have investigated either the cost or the benefit of mandatory audit firm rotation. Prior studies provide only indirect evidence on the effects of audit firm tenure on audit quality/perceived audit quality. By discussing prior arguments, we examine how investors perceive the implementation of mandatory audit firm rotation in Korea. Using a unique and direct setting to examine our research question, we analyze the relationship between firms with mandatorily switched audit firms and the cost of equity capital from 2006 to 2008. We find that the mandatory change in the auditors has a negative association with the cost of equity capital. The results are robust to using the arithmetic mean of the cost of equity capital, lagged control variables, and the manufacturing industry effect. The results indicate that investors perceive that mandatory audit firm rotation provides an environment for qualified audits by enhancing auditor independence and skepticism, and thus decreases the cost of equity capital. This study helps to improve our understanding of the impact of mandatory audit firm rotation the information risk evaluations and provides political implications for policy makers by showing the benefit of mandatory audit firm rotation.