PURPOSE: To produce the title slurry at high apparatus durability and reliability without being accompanied by roll crusher damaging, combustion choking accident, etc., by coarsely crushing coal, crushing it to grain and feeding grain coals through a specially installed coarse grains and foreign matter remover to a roll crusher.

CONSTITUTION: The coal fed from a banker 1 is coarsely crushed by a coarse crusher 2 and fed through a coal feed line 4 into a crusher 3 such as a wet type tube mill. The crushed coal is mixed with the additive and water fed through a line 6 from an additive tank 5 and crushed, thereby preparing a coal-water slurry. This slurry is introduced through a feed line 7 into a strainer 14 which is a coarse grain and foreign matter remover provided with a cylindrical screen 14a being a porous member having a vast plurality of through holes with a diameter which is larger than the max. grain size of the grain size distribution necessary for the product slurry but is smaller than the grain size of foreign matter etc. to be caught by the screen. From the strainer 14, rigid or soft foreign matter is discharged through a foreign matter discharge line 20, coarse grain coal is returned through a coarse grain coal feeder 16 and a line 17 to the crusher 3, and the slurry is fed to a roll crusher 8, whereby crushing into desired grain size is conduced.