Embodiments of the present invention help to suppress performance degradation in an actuator of a disk drive device when attaching a damping member to a single surface of an arm. According to one embodiment, in a HDD a damping member is attached to a single surface of an arm. A shape of an inner arm is asymmetric with the center position between disks. Specifically, the thickness from a center position between the disks to the damping material attaching surface is thinner than the thickness from a center position between the disks to an opposite surface of the damping member attaching surface. This suppresses deformation of the vibration mode in the case that the damping member is attached to the single surface of the arm.