Realization of a precise beam handling is strongly required in future accelerators such as linear colliders (LC) and X-ray free electron lasers (XFEL). The key component to realize a precise beam handling is a high resolution beam position monitor. An RF cavity type beam position monitor (Cavity BPM) is a candidate to measure the beam position in nano-meter resolution. In this presentation, activities of cavity BPM R&D at KNU (Kyungpook National university) as well as Fermilab will be described.