Bio-mass fuel gas is very important because bio-mass gas is renewable and carbon free. Especially, woody chips are very popular and are not used efficiently. Gasifier makes the producer gas from woody chips. Conventionally, dual fuel engines are used to generate electricity by producer gas and light oil. As the dual fuel engine can run under the low heating value gas, dual fuel engine is very useful. As light oil is fossil oil, it is not carbon free. If bio-mass gas engine can run only by producer gas, this power unit is carbon free. As the heat value of producer gas is very low and fluctuates always, bio-mass gas engine should be controlled A/F precisely. As the producer gas contains of hydrogen from 15 to 18%, NOx should be higher on concentration of 15 % hydrogen. Output of bio-mass gas engine should be low because of low heat value of producer gas. The three way catalyst can reduce NOx and CO. Stoichiometric mixture can make output higher than lean burn. Stoichiometric bio-mass gas engine has not developed yet now. Stoichiometric bio-mass gas engine was made as prototype and tested with the gasifier of wood chips. The type of the bio-mass gas engine are 4 cycle, water cooled. The displacement is 3.3L with natural aspirated. The number of cylinders is 4cylinders. The output is 20kW at 1900 rpm. This paper reported a study of stoichiometric bio-mass gas engine by using producer gas from woody chips.