To see that a molten metal leakage sensor does not operate even if a low boiling point matter such as zinc or the like permeates into the texture of a lining material, by using a glazing sleeve material, where ceramics glaze at a specified temperature or over is applied, for the interior face of an outer sleeve, and putting the permeability at the inner surface of this outer sleeve at a specified value or under.

The inner surface of an outer sleeve is made an inner surface glazing sleeve material where heat-resistant ceramic glaze at 500°C or over is applied, and the permeability at the inner surface of this outer sleeve is made 10 cm.cm/cm2.g/cm3.sec or under. Such an outer sleeve is installed at the sidewall on a furnace body side, and on its inside, a dry monolithic material is laid, using a former. Hereby, the nonconformity by the permeation of zinc can be solved. What is more, the outer sleeve can be used many times so long as there is no damage, it leads to the reduction of the cost of a furnace material for replacement. Moreover, the outer sleeve is a low hot linear expansion material, and has high quality, and it can lower the degree of damage.