[en] This is an interim report on conceptual design of the JT-60 neutral beam injection system. Requirements for the JT-60 neutral beam injector are injection of a 20 MW neutral hydrogen beam into the plasma in the vicinity of energy 75 keV as long as 10 sec, keeping thermal gas flow rate into the torus vacuum chamber below 15% the neutral beam flux. On the basis of these requirements and recent results of research and development of ion sources and beam line components, system conceptual design is now proceeding. Scale of the JT-60 neutral beam injection system is discussed, indicating also future problems. (auth.)