In 2020, a plan to revise the disclosure act of report on bulk holdings was implemented. The purposes of holding stocks in bulk have been subdivided into the simple investment, general investment, and management participation. If shareholders report general investment objectives for investment purposes,shareholder activism is possible. Thus the reported company may have a governance improvement effect. This study analyzed market reactions when changes were made for general investment purposes from simple investment purposes. This study analyzed market reactions when bulk-holding investors made changes for general investment purposes from simple investment purposes. As a result of the analysis, firms that have changed holding objectives have an average abnormal return of 0.4%p from one day before the date of disclosure until one day after the date of disclosure. This effect, if disclosed by the National Pension Service, results in a higher average abnormal return of 0.7 percent Next, we analyzed the investors’ transactions based on the disclosure date. Individual investors’ trade imbalance rises after the disclosure, and institutional investors’ trade imbalance falls. These results seem to be due to individual investors’ expectations for improved corporate governance in the future. Besides, this study shows that a short-term decline in performance may occur five days after the announcement of changes in investment purposes. This study contributes to the literature on the announcement effect of the public pension fund and the literature on governance improvement disclosure through hand-collecting data. On the other hand, this study was conducted shortly after the revision of the act of report on holding stock of bulk was implemented, and there are limitations that lack time series to measure the long-term performance of the announcement effect.