Global warming caused by greenhouse gases are currently a significant problem in the world. Hydrogen is regarded as one of the possible sources of energy for the future. Hydrogen fueled engines emit no carbon dioxide as tank-to-wheel. Hydrogen engines can reduce greenhouse gases in comparison to engines fueled with fossil fuels. A pre-mixed hydrogen-fueled engine, specifically, can be put into practical use in a short period of time from a technical point of view. However, there are some technical issues, such as backfiring and low power output to resolve. With the aim to put a pre-mixed hydrogen-fueled engine for trucks and buses into practical use, it is necessary to prevent backfiring and to develop a high output engine. A diesel engine modified as a pre-mixed hydrogen-fueled engine was equipped with a variable geometry turbo-charger for higher output. As a high pressure turbo-charger induces more backfiring, this study shows how to optimize an inlet system and an ignition system to prevent backfiring. In the results, engine was successful in increasing engine output without creating greater backfiring. This engine was installed in a microbus and was put into practical use. The microbus has been in use for two years and has travelled over 15,000 km.