A manufacturing method of a write portion for a thermally assisted magnetic head slider includes providing a write portion including a write element, a waveguide, and a plasmon unit; lapping opposed-to-magnetic recording medium surfaces of the write element and the waveguide, and an near-field light generating surface of the plasmon unit; only forming a carbon layer on the opposed-to-magnetic recording medium surface of the write element. Corrosive elements in the write portion can be prevented from being corroded and the write element can be prevented from being worn and abraded not only, stable thermal ability for a plasmon unit can be maintained but also.