A disk drive device comprises a rotor on which a recording disk is to be mounted and a fixed body rotatably supporting the rotor through a bearing unit. The rotor includes a projecting portion configured to fit into a central hole of the recording disk, a clamper configured to be fixed to the projecting portion, and a seating portion provided radially outward of the projecting portion. The projecting portion and the seating portion are configured such that the seating portion moves with respect to the projecting portion by fixing the clamper to the projecting portion with the recording disk being in between the clamper and the seating portion.