Embodiments of the present invention provide a magnetic disk unit capable of attaining miniaturization, lower cost, lighter weight, lower profile, and higher density. According to one embodiment, only a carriage and a spindle motor among respective constituent components of a hard disk drive (HDD) are securely attached to a support plate made of a hard metal material higher in rigidity than a shroud. All the constituent components of the HDD, except the carriage, and the spindle motor, (a voice coil motor, a ramp, a latch lever, an HDD connector and so forth), that is, the respective constituent components of the HDD, of which assembling precision, rigidity, and so forth are not required, are attached to the shroud small in wall-thickness, and lighter in weight, formed of a resin material such as plastics and so forth.