PURPOSE: To hold saccharide rate at a predetermined value by inputting head obtained by inputting saccharide rate and temperature of stock in a metering cup and the rate to obtain a correction value of predetermined amount of stock, and outputting a difference between the predetermined amount of the corrected stock and the head to a metering controller as a set discharge amount.
CONSTITUTION: Saccharide rate of stock of a metering cup 3 is detected by a saccharide rate detector 10, and the temperature of the stock is detected by a temperature detector 11. These outputs are input to a head calculator 12, which determines stock dynamic viscosity and specific weight by a built-in table from the rate and temperature of the stock to obtain the head. The output of the detector 10 is input to a stock predetermined amount corrector 13, which calculates the correction value of the stock predetermined amount. An adder 14 adds the predetermined amount input from a metering controller 6 and the output of the corrector 13 to calculate a correction stock predetermined amount. A subtracter 15 inputs the output of the adder 14 and the output of the calculator 12, and outputs (correction stock predetermined amount-head), i.e., set discharge amount of a drain valve 7.