The present invention provides a biomass gasification device that optimizes the pyrolysis temperature of biomass, the reforming temperature of pyrolysis gas, and the atmosphere thereof to generate a reformed gas containing a large amount of valuable gas. The present invention related to a biomass gasification device that is provided with a biomass pyrolyzer, a pyrolysis gas reformer, and a pyrolysis gas introduction pipe, wherein: the biomass pyrolyzer is further provided with a heat carrier inlet and outlet ports, and performs pyrolysis on the biomass by heat of the heat carrier; the pyrolysis gas reformer performs steam-reforming on pyrolysis gas generated by the pyrolysis of biomass; the pyrolysis gas reformer is further provided with an air or oxygen blow-in port; and the pyrolysis gas introduction pipe is provided on the biomass pyrolyzer-side surface below the upper surface of the heat carrier layer formed in the biomass pyrolyzer.