Embodiments in accordance with the present invention relate to methods wherein when a main pole is processed by using an ion milling technique, a re-adhesion layer created on the side face of the resist mask is removed with certainty. In one embodiment, an inorganic insulator from 5 nm to 100 nm which is soluble in an alkaline is arranged between the main pole material and a mask for processing the main pole material, and the main pole is processed by ion milling. After this process, the mask is peeled off, a surface treatment is performed by using an alkaline solution, resulting in the re-deposition film being removed.