Embodiments of the invention permit a magnet-based actuator lock mechanism to operate smoothly in a magnetic disk drive that uses a base made of a magnetic material. In one embodiment, the base to be used is made of a magnetic material. The actuator lock mechanism includes a rotatable arm that retains a magnet. A magnetic attraction force, which is oriented toward the base as indicated by an arrow, is generated in the magnet. The base is provided with a cut to reduce the attraction force. The cut is covered with a sealing material to maintain internal airtightness. The actuator lock mechanism may be, for instance, an eddy-current latch, inertia latch, or magnetic latch.