Abstract: A pre-tearing device for producing coarse flour out of bale plates of flake-dried wood pulp. The pre-tearing device comprises a feeding device for the plates and a rotating cylinder the surface of which is provided with spikes. The feeding device is arranged to feed the plates to be torn against the surface of the tearing cylinder in a direction that deviates from a direction perpendicular to the surface of the tearing cylinder. The spikes are arranged on the cylinder surface as two spirals rotating in opposite directions in relation to each other.