We presented a new pretreatment method for producing a clean coal under mild conditions, that is the skimming of coal by solvent below 350℃. To clarify the validity of this method, we examined the effect of coal type on the extraction yield and the quality of the extract produced. 14 kinds of coals were extracted by tetralin, tetralin/m-cresol=7/3 mixture, and a coal derived oil (carbol oil) under 10MPa at 350℃. Almost all sub-bituminous coals and lignite examined were extracted by 80% in carbol oil at 350℃, and all extracts were completely soluble in the solvent even at room temperature. The quality of the extract was examined from the viewpoints of mineral matter and sulfur contents. It was found that the extract was almost free from mineral matters. The extract obtained through tetralin extraction was almost free from sulfur. Thus, it was clarified that the proposed method was effective to produce a large amount of clean coals containing little mineral matters and sulfur under mild conditions.