PURPOSE: To keep the supply of lubricant sufficient by forming the inside of a bearing housing with an oil mist chamber storing leakage oil and seal air from labyrinth seals, and thereby forming an air discharge port and a lubricant discharge port at the upper end section and the bottom section of the chamber respectively.

CONSTITUTION: When lubricant supplied from a lubricant supply pipe 21 to a lubricant passage 10 within a bearing housing 5 passes through a circular cooling passage 45, it is then supplied to a bearing section 3 while a gap sensor 42 is being cooled. After it has been used as lubricant, it is stored at the bottom section of an oil mist chamber 15, so that it is discharged out of a lubricant discharge port 20 through a lubricant return auxiliary pipe 23 and a lubricant return pipe 25. Meanwhile, seal air from a seal air supply pipe 34 passes through a seal air supply passage 40 within the wall of the housing 5, and it is supplied to a space S between both of labyrinth seals 6a and 6b, so that it is thereby supplied while being turned out to be seal pressure. Air leaking out of the seal 6b is stored in the upper section of the chamber 15, and it is concurrently separated from lubricant so as to be discharged outside out of an air discharge port at the upper section through an air discharge pipe 33.