PURPOSE: To stably produce a sintering raw material having an optimum grain size distribution by adjusting the moisture of a dust mixture with the sintering raw material until a prescribed value is attained at the time of mixing wet dust and dry dust and pelletizing the sintering raw material.

CONSTITUTION: The wet dust 2 in a thickener 4 is dehydrated by a filter 8 and is supplied to a mixer 12. The dry dust 14 in a tank 18 is supplied via a conveyor 20 to the mixer 12. The dust mixed in the mixer 12 is dried and pelletized by a rotary dryer 24 and the pellets are fed to a sieve 40. The plus sieve is returned via a crushing machine 42 to the mixer 12 and the minus sieve is fed to a sintering furnace. A moisture meter 28 is provided to a discharge side conveyor 22 of the mixer 12 at this time and the moisture in the sintering raw material is adjusted to about 16W20%. Part of the sintering raw material is separated by a damper 28 and is returned to the mixer 12 when the amt. of the dry dust necessary for the adjustment runs short. The moisture 36 is provided to the conveyor 26 to detect the moisture of the sintering raw material. The combustion with a burner 38 of the rotary dryer 24 is then controlled until the moisture attains about 6W20%.