PURPOSE: To provide a solid fuel combustion device having spiral rotary grid mounted as a grid by a method wherein a cylindrical secondary combustion area having the circumferential wall with a secondary combustion air inlet port for causing a circulation flow to be generated upwardly is arranged at the upper part of the primary combustion chamber.

CONSTITUTION: Solid fuel stored in a fuel-storing tank 23 is fed through a fuel- supplying port 15 into a primary combustion area 13 by a specified amount of fuel supplying device 14, and both flame and high temperature gas are pushed upwardly from the inside of the spiral grid through steps of drying, dry distillation and combustion at the outer circumference of a cylindrical spiral grid B. Slags and ashes are dropped downwardly and transmitted from a slag discharging shoot 19 toward a slag discharging feeder 5. Since the spiral grid is rotated by a horizontal rotary mechanism, the fuel is agitated by agitator blades which are integral with the grid and then the fuel is ignited with primary combustion air fed through the air-flowing port 18. The combustion gas directed from the grid upwardly is ignited in a secondary combustion in a secondary combustion area with air fed through the secondary air- flowing port 21 and then a hot temperature flame more than 1,200°C is discharged through the upper discharging port.