The present invention relates to an apparatus for supplying bottom-blown gas through a porous plug in a ladle and for molten metal refining. A gas supply pipe 3 is connected to a bottom-blowing porous plug 2 attached at the bottom of a ladle 1. An accumulator tank 11a, is provided in parallel with the gas supply pipe 3. The bottom-blown gas is accumulated in the accumulator tank 11a, and blown into the ladle 1 to agitate the molten metal through the gas supply pipe 3 during refining. After the refining is finished, the switching valve 4 of the gas supply pipe 3 is closed, the switching valve 4a of the accumulator tank 11a is opened and the bottom blowing of a small amount of gas is supplied, and the blowing apparatus 10 is separated from the gas supply source 6 at joint 5. The bottom blowing of a small amount of gas for a long period of time prevents the molten metal from permeating into the ventilating pores of the bottom blowing porous plug after the refining, so that the solidification of molten metal in the ventilating pores of porous plug and the clogging of the pores can be avoided. Thereby, the repeated use of porous plug is made possible without the replacement of the porous plug.