A hydrogen powered vehicle system consisted of LH2 tank high pressure LH2 -pump, a device to inject hydrogen onto the hot surface, and ignitor in turbo-engine of CR 12:1 had been developed by Musashi Institute of Technology- Recently the authors applied this system to a medium duty truck produced by Hino Motors Ltd. Then following improvement were required. (1) Gas tightness and endurance of hydrogen injector were improved by the selection of material, size, finishing and by suppling a small amount of lubricating oil. (2) Mixture formation of the injected hydrogen with the compressed air was improved by tuning up the size and number of the nozzle holes and injection timing with the hydraulic pump and valve. (3) A small amount of hydrogen was supplied into the intake manifold. It reduced the combustion noise and also it recovered the evaporation loss in the LH2 -tank.