This study analyzed the impact of the divergence between cash flow rights and voting rights (ownership wedge) of owner-managers on research and development (R&D) investment. While R&D investment can bring substantial wealth to a firm if successful, its outcomes are uncertain, making it susceptible to the influence of managers' risk preferences. In owner-managed firms, agency problems arise between the owner-manager and outside minority shareholders, and these problems can be exacerbated when the divergence between the owner-manager's cash flow rights and voting rights is large. That is, as the divergence between cash flow rights and voting rights increases, the moral hazard of owner-managers may intensify, and it was predicted that even when the magnitude of the ownership wedge is identical, a lower level of cash flow rights would have a negative impact on R&D investment aimed at enhancing firm value. The empirical results showed that the ownership wedge had a negative impact on R&D investment in the subsample with low cash flow rights, supporting the hypothesis. This indicates that the impact of the ownership wedge on R&D investment can be identified when controlling for the level of cash flow rights, and can be interpreted as evidence that low cash flow rights intensify the moral hazard of owner-managers. Furthermore, additional analysis separating cash flow rights and voting rights confirmed the entrenchment effect of voting rights, yielding results that support the negative effect of the ownership wedge.