PURPOSE: To realize a low NOx and a reduction in non-ignited substance by a method wherein a thermal insulation material is supplied on a solid fuel in an intermediate flow area during movement of a stoker and the solid fuel is supplied to the thermal insulation material and then combustion is carried out.

CONSTITUTION: Coal 7 preburns as a procombustion zone 14 at an upstream side from an upstream position 11 of a stoker and may act as a pilot flame in respect to the downstream side from the position 11. New thermal insulation material 12 and now coal 13 are fed onto the thermal insulation material 6 and coal 7 acting as pilot flame at the upstream position 11. Combustion air 15 flows as indicated by an arrow. This air shows an air fuel ratio of less than 1 while passing through the thermal insulation material 6, coal 7, thermal insulation material 12 and coal 13, its temperature is kept high while self-burning with the thermal insulation material 6 and the coal 7 and then smoke-dried. That is, the fresh combustion air is blown into the upper part of the downstream side of the upstream side of the stoker 11 to make complete combustion at the gas cumbustion position 16.