A method for burning woody biomass fuel exhibiting a grain size distribution of 2mm or under, comprising burning the biomass fuel using a biomass combustion burner, the biomass combustion burner comprising: a biomass fuel jet nozzle having a bent section and a fuel jet port that jets biomass fuel conveyed by primary air; a secondary air nozzle having a secondary air jet port that surrounds an opening in the fuel jet port, the secondary air nozzle jetting secondary air; and a tertiary air nozzle having a tertiary air jet port that surrounds the secondary air jet port, the tertiary air nozzle jetting a swirl flow of tertiary air, wherein the biomass combustion burner includes a swirler disposed at a center inside the biomass fuel jet nozzle, the swirler changing a biomass fuel stream drifted by the bent section into an axially whirling swirl flow to thereby make a fuel concentration lower on a pipe axis side and higher on an outer circumferential portion side, and includes a degree-of-swirl adjusting plate disposed on a pipe inner wall immediately upstream of the fuel jet port, the degree-of-swirl adjusting plate reducing a degree of swirl of the fuel stream that jets from the fuel jet port, thereby optimizing a fuel concentration distribution, and an opening in the secondary air jet port and an opening in the tertiary air jet port are adjusted to reduce an amount of the secondary air and a buffer stream is thereby formed between the fuel stream and a tertiary air stream, and wherein the biomass fuel is burned by supplying the biomass combustion burner with a fuel stream that contains the woody biomass fuel exhibiting a grain size distribution of 2 mm or under, the woody biomass fuel being conveyed by the primary air, the fuel stream having a flow velocity of from 15 m/s to 25 m/s, and by supplying the secondary air and the tertiary air such that: the primary air has an A/C value that is not less than 0.8, and not greater than proportional distribution between A/C 2.5 in a quantity of fuel of burner rating and A/C 1.5 in a quantity of fuel of 60% of the burner rating, wherein the A/C value is a ratio of primary air flow rate (Nm 3 /h) to fuel (kg/h). a biomass fuel jet nozzle having a bent section and a fuel jet port that jets biomass fuel conveyed by primary air; a secondary air nozzle having a secondary air jet port that surrounds an opening in the fuel jet port, the secondary air nozzle jetting secondary air; and a tertiary air nozzle having a tertiary air jet port that surrounds the secondary air jet port, the tertiary air nozzle jetting a swirl flow of tertiary air, wherein the biomass combustion burner includes a swirler disposed at a center inside the biomass fuel jet nozzle, the swirler changing a biomass fuel stream drifted by the bent section into an axially whirling swirl flow to thereby make a fuel concentration lower on a pipe axis side and higher on an outer circumferential portion side, and includes a degree-of-swirl adjusting plate disposed on a pipe inner wall immediately upstream of the fuel jet port, the degree-of-swirl adjusting plate reducing a degree of swirl of the fuel stream that jets from the fuel jet port, thereby optimizing a fuel concentration distribution, and an opening in the secondary air jet port and an opening in the tertiary air jet port are adjusted to reduce an amount of the secondary air and a buffer stream is thereby formed between the fuel stream and a tertiary air stream, and wherein the biomass fuel is burned by supplying the biomass combustion burner with a fuel stream that contains the woody biomass fuel exhibiting a grain size distribution of 2 mm or under, the woody biomass fuel being conveyed by the primary air, the fuel stream having a flow velocity of from 15 m/s to 25 m/s, and by supplying the secondary air and the tertiary air such that: not less than 0.8, and not greater than proportional distribution between A/C 2.5 in a quantity of fuel of burner rating and A/C 1.5 in a quantity of fuel of 60% of the burner rating,