A storage device includes a storage medium; a rotating shaft; a head actuator pivotally supported about the rotating shaft; a head fixed at an end of the head actuator for reading/writing information from/to the storage medium; and a magnetic circuit having a magnetic member and a magnet connected thereto. The magnet has a magnetic characteristic corresponding to the inertia of the head actuator. The storage device further includes a coil fixed at the other end of the head actuator. The coil generates a driving force proportional to the inertia when an electric current is flown through the coil by interaction with the magnetic circuit. The driving force causes the head actuator to be driven to adjust the head to a target position on the storage medium. The magnetic member is configured as a single unit having a common dimension among a plurality of storage devices having different specifications.