Abstract. A high power neutral beam injector (NBI), each delivering a deuterium neutral beam of 16.5 MW at 1 MeV, has been designed for ITER. A key component of the NBI system is a high power beam source which produces a 40 A negative deuterium ion beams at the energy of 1 MeV. JAERI (Japan Atomic Energy Research Institute) has developed a vacuum insulated beam source (VIBS). The VIBS insulates the high voltage of 1 MV by immersing the ion source and accelerator in vacuum. So far the VIBS succeeded in acceleration of 37 mA beam up to 970 keV for 1 s. The achieved beam energy is nearly equal to the required value for the ITER NBI system. The negative ion source for the ITER beam source has been also developed. One of the key issues for the negative ion source is reduction of the operating pressure. By optimizing the filter magnetic field for negative ion production even at low pressure, a H- ion beam of 31 mA/cm2 was extracted at 0.1 Pa. Although the pulse length was very short (0.1 s) the ITER requirement on the current density was demonstrated at 1/3 of the ITER design pressure (0.3 Pa), which could reduce the heat loading on the accelerator grids.