Apparatus for refining fibrous material comprising first and second opposed refining disks, at least one of said first and second opposed refining disks being rotatable, a rotary shaft for rotatably mounting said at least one of said first and second opposed refining disks, a bearing housing for mounting said rotary shaft, a stand for stationary mounting of said bearing housing, said bearing housing including first and second bearings supporting said rotary shaft, said first bearing for at least carrying axial forces from said at least one of said first and second opposed refining disks and said second bearing for at least carrying radial forces therein, first and second bearing seats axially movable within said bearing housing, each of said first and second bearings being rigidly mounted in said first and second bearing seats, and prestressing structure mounted between said first and second bearing seats.