A hard disk drive device is provided, which is designed small, thin, and at low-cost. The hard disk drive device includes a case with an upright shaft, and a cylindrical hub coupled to the shaft. One end of the hub is closed by a thrust plate so that the hub has a bottomed cylindrical shape, and a hard disk is fixedly mounted on an outer peripheral part of the hub. An oil is filled in a clearance between an inner surface of the hub and an outer surface of the shaft, whereby a hydrodynamic radial bearing is formed between the inner periphery of the hub and the outer periphery of the shaft, and a hydrodynamic thrust bearing is formed between the top face of the shaft and the thrust plate. Between an outer peripheral part at the base end of the shaft and an inner peripheral part at the open end of the hub is formed a seal part in which a larger clearance is formed between the shaft and the hub than a clearance in the hydrodynamic radial bearing and in which the oil surface is positioned. An oil surface adjusting hole and a plug for sealing the hole are provided in the case opposite the seal part. A motor for rotating the hub is disposed between the outer peripheral part at the open end of the hub and the case.