Abstract: A swing-type actuator for use in a magnetic disk unit which includes a magnetic head; an arm supporting the head and a movable coil acting in a magnetic circuit. The movable coil is composed of a coil bobbin having a conductive wire wrapped around the bobbin. The bobbin is produced by injection molding into the bobbin of a thermoplastic resin having a flexural modulus of at least 8×102 kgf/mm2 and a heat deformation temperature of at least 200° C. under a load of 18.6 kg/cm2. A junction member to which the arm and the bobbin are integrally fixed by insert molding is made of the same resin as the bobbin or another thermoplastic resin being selected from the group consisting of a polybutylene terephthalate resin, a polyphenylene sulfide resin, a polyamide, a polyether ether ketone resin and thermotropic liquid crystal polymer.