A gasification furnace 2 is divided into a plurality of gasification furnace units 2a and 2b each of which has an inlet 15a, 15b on a lower portion at a longitudinally upstream end in a direction of travel of raw and bed materials and has an outlet 16a, 16b on an upper portion at a longitudinally downstream end in the direction of travel. The outlet 16a is connected to the inlet 15b. The inlet 15a is fed with a raw material and a hot bed material from a materials separator 8. The inlet 15b is also fed with the hot bed material from the material separator 8. The outlet 16b is connected to a combustion furnace 5.