To provide a stopper structure capable of preventing an axial rod from loosening in use and also preventing gas leakage from occurring when a gas is passed.

On the external face in the circumferential direction at the tip part of an axial bar 1 fitted to the fitting hole 2a of a stopper refractory 2, a first taper face 4a whose diameter expands toward the lower edge side in the axial direction of the stopper is formed. Further, a second taper face 4b confronted with the first taper face 4a is formed at the inside face of the fitting hole 2a of the stopper refractory 2, and the axial bar 1 is tightened to the stopper refractory in such a manner that the first taper face 4a and the second taper face 4b are confronted and tightly stuck. Then, regarding the shape of the tip part of the axial bar 1, provided that the length from the position of the upper end face 2S on the stopper refractory of the axial bar 1 to the origin position of the first taper face 4a is defined as A, the outer diameter of the origin position of the first taper face 4a is defined as D, and the taper angle of the first taper face 4a is defined as , the relation of tanD/2A is satisfied.