The gasification gas produced in gasification furnace and the bio-mass gas collected from sewerage processing are receiving attention as renewable energy. The bio-mass gas of which the release calorific value is about a tenth of methane calorific value is the gas that contains much inert gas (N2, CO2). It is important that the bio-mass gas is utilized as one of renewable fuel. In this study the profiles of temperature and Carbon mono oxide (CO) concentration in the flame are measured. The blow off velocity is investigated with increasing the fuel velocity. We research into combustion characteristic and stability limits of the diffusion flame for utilities of biomass-gas.