PURPOSE: To prevent the non-resettable overpulverization state that the vertical mill may attain.

CONSTITUTION: A differential pressure between a supply side pressure of primary air 7 and the internal pressure of the vertical mill 1 is detected by a differential pressure gage 9. A deviation between a differential pressure set value signal 12 meeting the coal supply rate from a function generator 10 and a differential pressure signal 13 is determined by a subtractor 14. The rotating speed of a rotary classifier 8 is controlled by a control signal 17 from a function generator 16 based on this deviation signal 15, by which the coal output is regulated to control the amt. of the pulverized matter in the vertical mill 1 so as to be held at the normal amt. The overpulverization state is detected as an abrupt increase in the fluctuation width of the differential pressure by a computing element 20 if the overpulverization state exceeding the pulverization threshold is generated in the vertical mill 1 by a change in the hardness of the coal 3 to be fed. The rotating by a resetting signal 23 of a function generator 22 independently from the control by the control signal 17, by which the coal output is increased and the vertical mill 1 is reset to the normal pulverization state.