To prevent the movement of a slider to the data area of a disk which is caused by unexpected shake of an actuator in a shunting state due to an impact from the outside and reduce a crush stop.

When the impact is given to the actuator 22 on a shunting position, the moment of rotations is generated simultaneously in an inertia arm 7 and the actuator 22, the turning forces are competed with each other at the contact point C of an impact-transmitting part 7p on the side of the inertia arm 7 and an impact-transmitting part 22p on the side of the actuator 22, and thereby the impact is absorbed. Furthermore, the actuator is likely to excessively shake in the direction of load or unload over the intrinsic limit of the shaking, but the excessive shake of the actuator is prevented by letting a turning force-receiving part 7q on the side of the inertia arm 7 catch a turning force-transmitting part 22q on the side of the actuator 22 but not by the crash stop.