Abstract: Disclosed is an actuator of a hard disk drive. The actuator comprises a bobbin having an outside bobbin part made of plastic, an inside bobbin part of a lower height than the outside bobbin part, and a coil intervened between the outside bobbin part and the inside bobbin part by insert molding; a rib portion having a predetermined width and formed along a boundary region between the inside bobbin part and the coil such that it has the same height as the outside bobbin part; and a plurality of connecting portions having a selected width and each being branched from a center portion of the inside bobbin part and linked to a desired position on the rib portion such that it has the same height as the rib portion.