PURPOSE: To suppress the pressure variation owing to a poor condition of a main pipe pressure control system, by increasing the LNG flow rate of waiting carburetors adequately when the condition is tripped by using a single carburetor in a low load condition, in an LNG base where the number of LNG carburetors is controlled according to the load.

CONSTITUTION: The LNG delivered from an LNG tank 1 is gasified by carburetors 3 to 5, and after being collected in a vaporized gas main pipe 6, it is fed to the customers. In this case, according to the output of a detector P to detect the vaporized gas pressure in the main pipe 6, and a set value, a PID operation is carried out by a main pipe pressure regulating meter 7, and an LNG flow rate setting value signal is found by a carburetor number correcting operator 8, according to the resultant output. And when the condition is tripped by using a single carburetor in a low load condition, a MANUAL mode signal a is given to the main pipe pressure regulating meter 7 by a computer 18, until the waiting carburetors are converted to a load following mode through a rising mode, so as to 'cut' the main pipe pressure control operation, and the output of the main pipe regulating meter 7 is reset to a preset LNG flow rate value.