An apparatus (100) for reducing the size of material, comprising a milling device (17) containing a sieve (19) and a milling impeller (21) being rotated relative to the interior wall surface of the sieve (19); and a crusher device (40) containing a hollow part (1) of frusto-conical shape narrowing downwardly, a crusher spindle (5) rotatably mounted coaxial with the hollow part (1), at least one crusher impeller (9, 30) rotatably mounted on the crusher spindle (5), and a crusher driving device for rotatably driving said at least one crusher impeller (9, 30) relative to said first hollow part (2); wherein said milling device (17) is vertically connected below the crusher device (40), and wherein during a reducing operation, said material is first crushed by the crusher device (40) by rotating said at least one crusher impeller (9, 30), and milled by the milling device (17) by rotating the milling impeller (21).