A head stack assembly includes a head stack assembly main body moving a head across a disk, and rotating around a predetermined pivot shaft. The head stack assembly also includes a center of gravity compensation portion coupled to the head stack assembly main body and compensating for imbalances in the center of gravity of the head stack assembly main body to be not more than a reference imbalance value. The reference imbalance value is based on an imbalance value of the center of gravity of the head stack assembly main body measured with respect to a rotational center of the pivot shaft.