PURPOSE: To obtain high component recovery and a high deashing rate, by supplying residual coal obtained after the deashing operation in a deashing tank according to a flotation method to a coarse particle separator such as a screen to separate the coarse particle in the residual coal.

CONSTITUTION: The coal particles supplied to a deashing tank 8 as a slurry after wet grinding are separated into refined coal rising in a state of adhering to air bubble formed through a perforated plate 21 and residual coal. The residual coal 15 rich in ash is drawn out of the system from the lower part of the deashing tank 8 to be supplied to a screen 16 and fine particulate ash passes through the screen 16. The coarse particles remaining on the screen 16 are returned to a low concn. mill 5 through a coarse particle recovery line 18 and again ground. In this case, vibration may be applied to the screen 16 in order to increase separation speed.