This paper empirically analyzed the changes in value relevance of consolidated operating income reflecting consolidated entities using data from 2009 to 2013, spanning the periods before and after the adoption of IFRS. In 2011, the first year IFRS standards were applied, companies were allowed to autonomously choose their calculation methods for operating income, whereas in all other periods, operating income was uniformly determined according to the previous K-GAAP method. Therefore, this study analyzed which calculation method of operating income reflecting consolidated entities provides greater information usefulness from the perspective of stock market investors, using the Ohlson (1995) model in terms of relative value relevance. Through this analysis, the study sought to verify the effectiveness of the two policy changes related to operating income made by the supervisory authorities and the Korea Accounting Standards Board (KASB). The research hypotheses were established considering the intended direction when KASB changed the calculation method related to operating income. Specifically, it was hypothesized that consolidated operating income calculated under principle-based accounting in 2011, the first year of IFRS adoption (IFRS; 2011), would have lower value relevance than consolidated operating income calculated under K-GAAP in the pre-IFRS period (Pre-IFRS; 2009–2010) (Hypothesis 1); that consolidated operating income under the restored K-GAAP method in the post-IFRS period (Post-IFRS; 2012–2013) would have higher value relevance than consolidated operating income calculated under the initial IFRS standards in 2011 (Hypothesis 2); and that consolidated operating income under the restored K-GAAP method in the post-IFRS period would have higher value relevance than consolidated operating income under the previous K-GAAP method in the pre-IFRS period (Hypothesis 3). The main empirical results are as follows. First, for all three hypotheses, there were considerable differences between the regression results without standardizing the Ohlson (1995) model and the results after standardizing by prior-period stock price. These results suggest that because the Ohlson (1995) model verified through price-level models is analyzed using monetary variables, heteroscedasticity and scale effect issues argued in prior studies may lead to different results compared to those standardized by prior-period stock price (Kothari and Zimmerman 1995; Easton and Sommers 2003, etc.). Second, focusing on results standardized by prior-period stock price, for the full sample, only Hypothesis 1 was supported, while Hypotheses 2 and 3 were not supported. That is, the value relevance of consolidated operating income under the 2011 IFRS application based on principle-based accounting was found to be lower than that of K-GAAP-based consolidated operating income before IFRS adoption, indicating that corporate autonomy in calculating consolidated operating income rather diminished information usefulness (Hypothesis 1). Third, when the full sample was divided into KOSPI and KOSDAQ samples, Hypothesis 1 was supported for the KOSPI sample, while Hypothesis 3 showed evidence contrary to expectations. In contrast, only Hypothesis 3 was supported for the KOSDAQ sample. Therefore, for Hypothesis 3, unlike the full sample results, conflicting evidence was found across market types. Specifically, KOSPI-listed companies (KOSDAQ-listed companies) showed deteriorated (improved) value relevance of consolidated operating income in the post-IFRS adoption period compared to the K-GAAP period. This demonstrates that the mandatory adoption of IFRS accounting standards in 2011 and KASB's revision of K-IFRS in October 2012, which changed disclosure policies related to operating income, unfolded in different directions between the two markets that differ in governance structure. These research findings suggest that when supervisory authorities and KASB make policy changes related to K-IFRS accounting standards in the future, market-specific differences should be considered rather than applying a uniform approach to all listed companies as done previously.