PURPOSE: To instruct operator for the exchange of a vessel when it is fully filled with liquified gas by providing a control means and a sensor means and making the sensor means instruct for a prescribed operation of a control means for regulating gas pressure while controlling a valve, through an instructing means.

CONSTITUTION: A partition film 16 is sandwiched between a lower casing 14 and an upper casing 12 of a regulator 10. This partition film 16 is energized downward by a spring 40 arranged between a partition film board 41, which abuts on the partition film 16, and the casing 12. When the inner pressure of an exit chamber 19 is decreased, the partition film 16 is moved downward, a valve member 30 is moved away from a nozzle 24, and a valve 22 is opened. When the valve 22 is opened, pressurized gas is allowed to flow into the exit chamber 19 and when pressure is sufficiently high, the partition film 16 moves upward to close the valve 22. Concerning this instrument, a sensor means 50 is formed on the casing 12 so as to detect the motion of the partition film 16. The means 50 is mechanically connected to a move indicator 60 for forming a visual indication when a prescribed quantity of liquified gas is contained in the vessel.