An inertia latch mechanism has a latch arm, which latches a head actuator in a retreated position, and an inertia arm, which is rockably supported around a second pivot and rotates the latch arm to a latch position by rotating around the second pivot when subjected to an external force. A voice coil motor has a lower yoke, a top yoke, a voice coil attached to the head actuator and situated between the yokes, and a permanent magnet provided on at least one of the yokes. The top yoke has an arm retaining portion which extends overlapping the second pivot and that part of the inertia arm which is situated near the second pivot and restrains the inertia arm from slipping off the second pivot. The arm retaining portion is stepped to be one level higher than the top yoke.