A lubricant composition, including 20 to 99.5 wt. %, based on a total weight of the lubricant composition, of a base oil, the base oil having a solubility for ionic liquid methyltrioctylammonium-bis(fluorosulfonyl)imide of at least 3 wt. % at a room temperature of 20 C. The base oil contains a base stock A in a proportion of at least 50 wt. %, based on a total weight of the base oil, the base stock A having a solubility for the ionic liquid methyltrioctylammonium-bis(fluorosulfonyl)imide of at least 3 wt. % at a room temperature of 20 C. The lubricant composition further includes 0.5 to 80% wt. %, based on the total weight of the lubricant composition, of an ionic liquid whose anion is bis(fluorosulfonyl)imide.

[Object] To provide a fluid dynamic bearing filled with a lubricating oil composition containing a base oil and an ionic liquid, and to provide a spindle motor in which evaporation is suppressed in the lubricating oil composition provided in the fluid dynamic bearing by incorporating the fluid dynamic bearing in the spindle motor, and thus occurrence of a read/write error in an HDD can be suppressed, and a disk drive device including the spindle motor. [Solution means] A fluid dynamic bearing filled with a lubricating oil composition containing a base oil and an ionic liquid, wherein the ionic liquid contains at least one cation selected from the group consisting of a tetraalkylphosphonium cation and a tetraalkylammonium cation and at least one anion selected from the group consisting of an imide anion, a methide anion, and borate anions represented by formulae (C-1) to (C-3). (In the formulae, R.sup.9 and R.sup.11 each independently represent a linear or branched alkyl group, and R.sup.10 and R.sup.12 each independently represent a hydrogen atom or a linear or branched alkyl group.)

[Object] To provide a fluid dynamic bearing filled with a lubricating oil composition containing a base oil and an ionic liquid, and to provide a spindle motor in which evaporation is suppressed in the lubricating oil composition provided in the fluid dynamic bearing by incorporating the fluid dynamic bearing in the spindle motor, and thus occurrence of a read/write error in an HDD can be suppressed, and a disk drive device including the spindle motor. [Solution means] A fluid dynamic bearing filled with a lubricating oil composition containing a base oil and an ionic liquid, wherein the ionic liquid contains at least one cation selected from the group consisting of a tetraalkylphosphonium cation and a tetraalkylammonium cation and at least one anion selected from the group consisting of an imide anion, a methide anion, and borate anions represented by formulae (C-1) to (C-3). (In the formulae, R.sup.9 and R.sup.11 each independently represent a linear or branched alkyl group, and R.sup.10 and R.sup.12 each independently represent a hydrogen atom or a linear or branched alkyl group.)