PURPOSE: To save electricity for pumping power by combining pulp materials in a constant ratio by fixing a concentration detector and a combination control unit and by controlling drive of a plural number of pulp material feed pumps by a variable speed motor.

CONSTITUTION: When a material combination ratio is set by a combination ratio setter 15 and a total combination volume of pulp material is set by a total combination volume setter 17, outputs of these setters are input in a combination volume computer 34. Output of the computer 34 and an output signal of a concentration signal detector 15 are input in a combination volume computer 35 and a combination flow is determined. The output of the computer 35 becomes an input to a speed computing circuit 36 of a driving motor 4 for a pump 3 and a set speed is fixed. An output signal of the speed computing circuit 36 is input to a speed setting circuit 25 of a motor drive control unit 21 and a driver 4 is controlled at a set speed and pulp materials are controlled at the originally set combination ratio.