A coil bobbin is formed by injection-molding a thermoplastic resin (A) having an elastic modulus of 8 x 10<2> kgf/mm<2> or more, and a thermal deformation temperature of 200 DEG C or higher under a load of 18.6 kg/cm<2>. The bobbin and an arm are integrally fixed to the actuator of a disk unit by use of a coupling member made of a thermpolastic resin (B).
