To remotely melt a mushroom without using oxygen and to instantaneously open a tuyere for converter observation by a method wherein a solidified metallic substance formed in the vicinity of the inner wall interface of a tuyere for the internal state of a converter is irradiated with laser beams to effect melting and opening.

In opening of a mushroom 4, laser beams 3 of carbonic acid gas laser is transmitted through a window 9 arranged at an argon substitution box 7 and a dichroic mirror 10 and collected at the inlet of a pipe by a lens 5 arranged at the outside of the argon substitution box 7. A window 9 is formed of a flat plate and non-reflection coating for carbonic acid gas laser is applied on the two surfaces thereof, and a switch type mirror 6 is retreated to a position A at the time of opening. The laser beam 3 from the carbonic acid gas is transmitted to the mushroom 4 by utilizing a multireflection effect by the inner surface of the pipe. This constitution remotely and instantaneously opens the mushroom without using oxygen.