To reduce harmonic resonance accompanying oscillation of an inner ring and to attain stable operation by forming a clearance between the spherical surface on the outer diameter side of a bearing inner ring and the spherical surface on the inner diameter side of an outer ring, and detuning the oscillating natural frequency of the inner ring against the rotational frequency of a rotary shaft.

The radius of curvature of the spherical surface 24 on the outer diameter side passing the center Ob of a bearing inner ring 20 is set to be Ri, the radius of curvature of the spherical surface 25 on the inner diameter side 23 passing the center Op of a bearing outer ring 21 is set to be Ro, they are formed so as to be Ro-Ri>0, meanwhile a clearance Cr is formed between the radii of curvature Ri and Ro, so that the bearing inner ring 20 can oscillatably follow to the rotational displacement of a journal part. The clearance Cr is set to be a distance added with a surplus of about ±10%, so that the oscillating natural frequency fn of the bearing inner ring 20 can be detuned from N times and 1/N times such as 1/2fo times, to times, 2fo times the rotational frequency fo of the journal part. Hereby, a large-sized rotary machine can be operated further stably.