A write shield layer that forms a part of a thin-film magnetic head is set with respect to the widthwise full length W thereof lying substantially on an air bearing surface that is opposite to the recording medium such that when the full length W is trisected, the maximum thickness H.sub.1/3side thereof in a range of widthwise 1/3W size positioned at both ends thereof is larger than the average thickness H.sub.m of the whole write shield layer from the air bearing surface up to the rear (H.sub.1/3side>H.sub.m), so that the so-called external magnetic field resistance is improved, and inadvertent erasure of the information already recorded in the recording medium is avoided as much as possible. Besides, the PTP (pole tip protrusion) phenomenon arising from the generation of heat from coils, and external temperature changes can be held back.