Key requirements of engines for vehicles are large output power and high efficiency, low emission as well as small size and light weight. Hydrogen combustion engines with direct injection have the characteristics to meet these factors. Tokyo City University, former Musashi Institute of Technology, has studied hydrogen fueled engines with direct injection since 1971. The key technology in the development of hydrogen fueled engines is the hydrogen injector for direct injection with the features such as high injection rate, high response and no hydrogen gas leakage from the needle valve of the hydrogen injector. A common-rail type system to actuate the needle valves of the high pressure hydrogen injectors was intentionally applied to fulfill good performances such as large injection rate, high response and no hydrogen gas leakage. Eventually, high pressure hydrogen injectors have been developed for direct hydrogen engines at the injection pressure of 20 MPa at the maximum, capable of performing large injection rate, high response and no hydrogen gas leakage from the hydrogen needle valves. The leakage of hydrogen gas was not observed definitely for such time as 700 hours.