PURPOSE: To absorb and dissolve gaseous CO2 sufficiently in a liquid mixture by connecting a feeding pipe of gaseous CO2 and a feeding pipe of the liquid mixture to a producing tank separately.

CONSTITUTION: A liquid mixture is fed to a producing tank 18, and the pressure of gaseous CO2 passing through a CO2 feeding pipe 2 is set to a specified value by a reducing valve 3. Then, cooling operation of the producing tank 18 is performed using a cooling device. At the same time when the liquid mixture in the producing tank 18 begins to get cold, the gaseous CO2 becomes more easily absorbable in the liquid mixture. Therefore, the pressure of gaseous CO2 decreases below the specified value. When the pressure decreases to a certain degree, the liquid mixture is saturated with CO2. In this state, the pressure of gaseous CO2 supplied to the producing tank 18 is held at a specified value, and carbonated beverage in the producing tank 18 is discharged through a discharging cock 19.