A solid fuel producing apparatus that even when supply of raw coal (RC) and mixed oil (MO) and supply of slurry to subsequent steps are stopped because of troubling at evaporation step or later, etc., would prevent cloggings of heat exchanger and raw coal supply means. The solid fuel producing apparatus includes a mixing tank (1) for mixing porous coal with a mixed oil having heavy oil and solvent oil contents to thereby obtain a raw slurry; an evaporator (2) for processing evaporation of water from the raw slurry by heating the same to thereby obtain a dewatered slurry; a solid-liquid separator (3) for separation of the mixed oil and upgraded porous coal from the dewatered slurry; and circulation means (4) for returning the mixed oil having been separated and recovered by the solid-liquid separator to the mixing tank. The solid fuel producing apparatus is characterized by having a mixed oil heating heat exchanger (5) for heating the mixed oil to be returned to the mixing tank by the circulation means.