An apparatus is for dropping a liquified inert gas into a can immediately before rolling of the can, to apply an internal pressure to the can after can sealing. Liquefied gas is supplied from a liquified gas main tank (5) to a liquified gas storage tank (1) having a gas pressure lower than that of the main tank. The supply is controlled by a bucket or ball type float valve (15) to maintain a constant liquid level at all time. A given amount of liquified gas is dropped from a dropping nozzle (4) into a can by means of a dropping valve (3) actuated by a sensing signal produced when the presence of a can is sensed. The internal pressure of the storage tank is maintained constant by releasing vaporized gases within the tank through a regulating valve (13).; This released gas shields the liquified gas passing through the dropping nozzle to prevent vaporization of the gas and freezing of the nozzle. To prevent additionally the nozzle from being frozen, a portion of the nozzle may be made of a suitable synthetic resin.