PURPOSE: To make charging accurate and easy by performing subtraction by the weight (tare) of a container through an automatic arithmetic circuit.

CONSTITUTION: With cock 5 opened, cooler 7 to be charged is supplied with gas in in cylinder 4 via hose 6. The weight detection output of a load cell is amplified by amplifier 8 and then input to one amplifier 13 that calculates the net weight or charging weight. With change-over switch 12 placed at the total weight side, the total weight including the tare of cylinder 4 is displayed on digital display unit 16. Next, the tare value of cylinder 4 is set to digital switch 9 and change-over switch 12 is placed at the net weight side to perform subtraction by the tare at operational amplifier 13, so that the net weight will be displayed on digital display unit 16.