According to one embodiment, a method for manufacturing a thin film magnetic head includes forming on a substrate magnetic head portions having a magnetoresistive element and resistance detection elements for measuring an amount of polishing; slicing the substrate to form at least one row bar; polishing the ABS of each row bar; forming rails on the polished ABS; and cutting each row bar to separate each magnetic head portion. The step of polishing the ABS includes measuring a resistance of each resistance detection element and a resistance of each magnetoresistive element; calculating an offset value between the resistance detection element and the magnetoresistive element; and calculating a final resistance of the resistance detection element by using the calculated offset value. When the resistance of the resistance detection element reaches the final resistance, polishing of the ABS of the row bar is terminated. Other methods are presented as well.