In 2015, Kyoto University, Japan, adopted the Kyoto University Open Access Policy, which mandates faculty members to make their scholarly articles public on the institutional repository, Kyoto University Research Information Repository (KURENAI). In 2020, five years after the implementation of the open access policy, we investigated the effects of the same. This paper presents a bibliometric analysis to reveal the effects of open access, comparing scholarly articles deposited to the KURENAI with their counterparts (i.e., scholarly articles not deposited to the KURENAI) to examine whether a citation advantage exists. The analysis revealed that the KURENAI has contributed to increasing the number of citations of scholarly articles not co-authored with foreign researchers and scholarly articles in different fields. Thus, we argue that institutional repositories foster interdisciplinary research. We also observed that scholarly articles that are open access only on the KURENAI have been downloaded more frequently than those that are also open access on other platforms (e.g., open access journals and other repositories). Owing to a large number of submissions, it may take some time until a deposited article becomes available for access on the KURENAI. Accordingly, it would be helpful for researchers and libraries to introduce a system that, when processing deposited scholarly articles, prioritizes the publication of articles that are not openly accessible on other platforms.