The gasifier has a gasification reactor (32) including a pyrolysis unit (14), an oxidization unit (16), and a reduction unit (18). A supplying unit (10) supplies biomass into the pyrolysis unit. A conveying unit conveys the biomass by the pyrolysis unit. An opening (42) supplies gasification agent into the oxidization unit. A dissipation unit (20) drives off product gas (22) e.g. hydrogen gas, from the reduction unit of the gasification reactor. A supplying unit is opened to supply the gasification agent in a middle part of the oxidization unit.
