The present invention relates to a biomass gasifier capable of generating synthetic gas by pyrolyzing biomass. According to the present invention, the biomass gasifier comprises: a housing; an inlet of inserting biomass into the housing; a drying chamber prepared in the lower side of the inlet to dry biomass; a pyrolysis chamber prepared in the lower side of the drying chamber to pyrolyze by heating the biomass; a primary combustion chamber prepared in the lower side of the pyrolysis chamber to burn the biomass while air is supplied thereto; a reduction chamber prepared in the lower side of the primary combustion chamber to generate synthetic gas (2CO, H_2) as CO_2 and H_2O (Vapor) generated in a combustion process pass through a bed layer of biomass charcoal; a secondary combustion chamber prepared in the lower side of the reduction chamber to supply CO_2 and H_2O to the reduction chamber by generating CO_2 and H_2O while air is supplied to the biomass charcoal; a fixed bed installed in the lower side of the secondary combustion chamber to support the biomass charcoal, and having a plurality of through holes; an air supplier of supplying air to the primary combustion chamber; a gas receiving pipe of receiving synthetic gas generated from the reduction chamber; and an air inlet pipe of supplying air to the secondary combustion chamber.
