Provided are a viscous fluid-filled damper reducing the size of a disk device and achieving sufficient vibration-damping effects by preventing air from being invaded inside a closed vessel, and the disk device. The closed vessel 15 is formed to have a thinner shape, compared to conventional closed vessels. This reduces a mounting space of the viscous fluid-filled damper 14. Thus, the size of the disk device can be reduced. When a mechanical chassis 4 is relatively displaced with respect to a casing 7, an inner cylindrical part 16c positioned in the center and an inner edge portion of a cover part 17a bonded to the inner cylindrical part 16c are moved to a three-dimensional direction. Thereby, a bottom part 16b and a portion of the cover part 17a opposing to the bottom part 16b are interlocked, and along with this interlock, viscous fluid 10 filling the inner side of the closed vessel 15 is stirred. Therefore, vibration damping effects due to stirring of the viscous fluid 10 can be exhibited without providing a stirring cylindrical part projecting inwardly like conventional closed vessels.