PURPOSE: To sense abnormality in the clearance space of a bearing simply and certainly by installing a flow meter, which emits an abnormality signal when the sensed value lies outside the allowable range, in a gas supply path connected with a gas supply hole in a gas bearing, and connecting this flow meter to an alarm means via a control means.

CONSTITUTION: A flow meter 14 emitting an abnormality signal. when the sensed value lies outside of the allowable range, is furnished in a gas supply path 13 which is connected with gas supply holes 11 in a journal bearing 1 and a thrust bearing 2. Further to this flow meter 14, an alarm 16 is connected via a controller 15 to issue an alarm from an alarm device 16 when an abnormality signal is given. Thus any abnormality in the clearance space of the bearing is sensed simply and certainly.