Interest in carbon-fiber-reinforced plastic (CFRP) has been growing for the last several years. CFRP, a composite material made of carbon fibers and resins, has high mechanical characteristics and is well known as a difficult-to-cut material. During the process of drilling or cutting of CFRP, tool wear and delamination occur frequently. In this study, the authors developed a milling tool for CFRP using polycrystalline diamond, and the cutting performance of the developed tool was investigated.