PURPOSE: To enhance the sealing performance of a sealing structure for the gap between a housing and rotary shaft using a sealing member, by forming the housing with a coefficient of thermal expansion which is smaller than that of the rotary shaft.

CONSTITUTION: The rotary shaft 72 of a gas supply device for degasification is supported rotatably by a housing 71 with the aid of a bearing member 73, and a ring-shaped sealing member 74 is installed at the inside surface of the housing 71. The sealing member 74 is made, for example, of urethane and prevents a molten metal in a treatment chamber for degasification from flowing in the direction of the bearing member 73. Therein the coefficient of thermal expansion of the housing 71 (for example, carbon steel) is made smaller than that of the rotary shaft 72 (for example, austenite type stainless steel). When this sealing structure is heated, the rotary shaft 72 makes a thermal expansion in a greater rate than the housing 71, so that the sealing member 74 is pinched lay the housing 71 and rotary shaft 72 to lead to enhancement of the sealing performance.