To increase the classifying precision of pulverized materials to improve product quality.

A first pressure measuring instrument 18 is fitted on the sidewall of a pulverizing chamber 11, and based on the measurement results thereof, the opening degree of a discharged quantity control valve 30 is controlled. Here control is made so that static pressure in the pulverizing chamber 11 can be zero. In this way, a raw material 16 in the pulverizing chamber 11 is not influenced by anything except compressed air jetted from a pulverizing nozzle 12 and is pulverized under set conditions. Therefore, the pulverizing conditions are properly set to increase the classifying precision and to improve product quality.