PURPOSE: To blow an inert gas automatically into molten steel by mounting a ladle contg. molten steel on a carriage thereby communicating the gas supply pipe of the ladle with the gas supply pipe of the carriage and blowing an inert gas to the molten steel.

CONSTITUTION: A ladle B contg. molten steel is carried onto a carriage with a crane and the trunnion 10 of the ladle B is placed on the support base 4b on the carriage with the guide of the guide surface 5' of a guide frame 5. Then, the heat resistant packing 8 inserted into the port of the base 4 induces a compressive deformation with the weight of the ladle B, and the opening part at the top end thereof is brought into press contact with the bottom part of the trunnion 10, by which the opening part 11' at the top end of the gas supply hole 11 on the turnnion side and the gas supply pipe 9 on the opening part side of a port 5 are communicated with each other. An inert gas fed through the pipe 9 is supplied through the port 7, the hole 11, a supply pipe 12 and a porous plug 13 into the ladle B, whereby the gas bubbling of the molten steel is accomplished.