To provide a rotary shaft sealing device capable of coping with abnormality of an exhaust pump irrespective of a compact configuration.

Magnetic fluid ML is driven out of a storing part 2k in accordance with reduction of suction force of the exhaust pump P1, and a catching part 2m forms a magnetic circuit between an opening 2a and a rotary shaft 3 to catch the driven out magnetic fluid ML so as to bridge between the opening 2a and the rotary shaft 3. Consequently, even if abnormality occurs in the exhaust pump P1, the atmosphere in a housing 2 is automatically isolated to prevent a workpiece during processing from being damaged.