The internal accounting control system is a system introduced to enhance corporate accounting transparency and ensure reliability. In other words, firms that reported non-clean review opinions on their internal accounting control systems are operating their systems less efficiently compared to firms that reported clean opinions. Therefore, many prior studies have empirically demonstrated that external information users perceive firms that reported non-clean review opinions on their internal accounting control systems more negatively than firms that reported clean opinions. Based on prior research, this study examined whether firms that received non-clean review opinions due to structural problems in their internal accounting control systems have higher subsequent debt financing costs compared to firms that received non-clean review opinions due to deficiencies in account-level controls. Additionally, the study examined the impact on subsequent debt financing costs by major reasons for the adverse findings, in order to investigate whether the specific reasons cited in non-clean review opinions of the internal accounting control system affect the decision-making of bond market participants. To test this, the study targeted firms listed on the Korea Exchange that reported non-clean review opinions on their internal accounting control systems from 2006 to 2009, and 197 firm-year observations that met other sample selection criteria were used as the final analysis sample. The analysis results are as follows. First, among firms that reported non-clean review opinions on their internal accounting control systems, firms that reported function-level deficiencies had higher subsequent debt financing costs than firms that reported account-level deficiencies. Second, particularly firms that failed to submit their internal accounting control system operation reports to auditors, and firms that received non-clean review opinions due to deficiencies in the management, establishment, and documentation of the internal accounting control system, were found to have higher subsequent debt financing costs. This indicates that bond market participants perceive firms reporting these two types of deficiencies negatively.