[en] JAERI has been proposed a high intensity proton linear accelerator to be utilized in future accelerator-driven Partitioning and Transmutation (P and T) system. The R and D of the high intensity proton accelerator was started in 1991 as one of the approaches for the OMEGA program in Japan. The first phase of the R and D has been made successfully on the components of the front-end part of the accelerator i.e., an ion source and RFQ, resulting in the peak current of 70 mA with duty factor of 7 ∼ 10 % operation was obtained at the energy of 2 MeV after the RFQ acceleration. In these years, JAERI has been planned the Neutron Science Research Program (NSRP) for exploring basic researches and nuclear waste transmutation technology based on a next generation spallation neutron source driven by the high intensity proton linac. The conceptual design of the high intensity proton accelerator is rearranged slightly to achieve various operation modes in the NSRP. The second phase R and D has been started for the study of whole accelerator system with 1.5 GeV and 10 mA, beam power of about 15 MW. This report describes the summary of the first phase R and D and the present status of the second phase development of the high intensity proton linear accelerator. (authors)