The planned development of a hydrogen ICE system for trucks is one of the technological candidates for air pollution reduction and global warming prevention for the large-sized (heavy-duty) trucks supporting Japanese freightage. This project is the first to develop a DISI multi-cylinder hydrogen ICE system aimed at combining high power output and low NOx generation.The results of the first activities of the project are as follows: 1) High-pressure hydrogen gas direct injectors with a compact body size and control responsiveness that are suitable for the transient driving of the DISI multi-cylinder hydrogen engine were developed. 2) For limited driving conditions, a combustion control strategy of the DISI hydrogen ICE that balances low NOx emission with high power output was founded. 3) The performance of the DISI multi-cylinder hydrogen ICE system was evaluated, and the target output was obtained. 4) JE05 mode transient emission testing of the DISI multi-cylinder hydrogen ICE system with NSR catalyst and DOC was carried out; it showed emissions lower than those specified by the JAPAN 2009 emission regulations.