We analyze the influence of ownership structure on the R&D (research and development) investment of start-up firms. Previous studies on the relationship between ownership and R&D have targeted on large listed firms and focused on ownership concentration, regardless of the types of large shareholders. We argue that shareholder's type is an important factor of R&D investment under asymmetric information, and that R&D projects, particularly those of start-up firms, strongly depend on the financing from venture capitalists (VCs). Using a unique dataset of Japanese start-up firms, we find that the shareholding by VCs have, in fact, positively affects the R&D investment and that the impact of VCs funding is especially large when the shareholding by the lead VC exceeds 10%.