A method of mixing pulverulent materials and a device for practicing the method. In this method, the pulverulent material constituting a main material is continuously fed to a conveyor duct connected to a molding machine in fixed quantities while air is being fed to under pressure or drawn from the duct and simultaneously the pulverulent material constituting compounding ingredient material is fed to the duct at a specified value so that a mixing ration is maintained at a specified value. And in the method, a mixing ratio is changeable by variably controlling the amount of supply of compounding ingredient to the main material while feeding air into the duct or drawing air from the duct. In addition, the device is constructed of a pneumatic closed loop duct type and comprises a closed looplike duct, a pulverized reclaimed material feed unit, a virgin material feed unit, and a control means for regulate a mixed ratio.