[en] Modification of JT-60U to a superconducting device (so called JT-60SA) has been planned to contribute to ITER and DEMO. The main missions of JT-60SA are to optimize the operational scenarios of ITER in break-even class plasmas and to establish high beta steady-state operation for DEMO. Then, the design requirements are to have capability of steady state high beta plasma with full non-inductive current drive for more than 100 s. To achieve this requirement, the NBI system is required to inject 34 MW for 100 s. The upgraded NBI system consists of twelve positive ion based NBI (P-NBI) units and one negative ion based NBI (N-NBI) unit. The injection power of the P-NBI units are 2 MW each at 85 keV, and the N-NBI unit will be 10 MW at 500 keV, respectively. There are three types of P-NBI units (perpendicular: 8 units, co-tangential: 2 units, counter-tangential: 2 units) to control deposition profile and plasma rotation. The beam line of the co-tangential N-NBI unit is shifted downward from the equatorial plane by ∼ 0.6 m to drive off-axis plasma current so as to produce reversed shear with a high bootstrap current fraction. The critical issue of the modified NBI system is to extend the pulse duration up to 100 s. In the P-NBI unit, long pulse operation of P-NBI unit at 2 MW for 30 s has shown that the temperature rise of the cooling water in the ion source is almost saturated at less than 10^oC after ∼ 15 s, so the present ion source of P-NBI may operate for 100 s. In the preliminary study, the present high voltage DC power supply for P-NBI unit can drive the ion source for 100 s by modifying some resistances and employing active cooling of the inner conductor in the high voltage feeder duct. The available beam voltage of the present N-NBI is less than 400 keV, so the main issue of N-NBI unit is to improve the voltage holding of the ion source up to 500 kV. A modification of the accelerator such as the insulator structure is under consideration. The present acceleration power supply of 500 kV, 64 A with an inverter switching system will also be modified to extend its pulse duration from 10 s to 100 s by adding more converter-inverter components. The last item is shielding of the leakage magnetic field of the JT-60SA. The leakage field will be about five times larger from the JT-60U, so attachment of high permeability metal on the ion tank is required, in addition to strengthening the canceling coils. The details of this technical design of NBI system for JT-60SA will presented. (author)