The invention provides a magnetic head stack assembly capable of mounting a slide piece on a suspension rack fixed on an E block; the magnetic head stack assembly making device comprises elements capable of executing the following steps: relatively moving the suspension rack and an optical axis converter in a direction parallel to the central plane of a pair of suspension racks, so the optical axis converter can enter the pair of suspension racks; using a camera with a shooting optical axis bended by the optical axis converter to take two reference marks; using the two reference marks to detect a slide piece carrying position.