A grease composition includes alkylnaphthalene as base oil and a urea compound as thickening agent. The thickening agent is an alicyclic aliphatic diurea compound contained at a ratio of 4 mass % to 10 mass % based on the total mass of the grease composition. A pivot assembly bearing device is provided with rolling bearings filled with the above grease composition. A hard disk drive device is provided with a swing arm which is swingably supported by the pivot assembly bearing device.