Provided is a thin film magnetic head which enables both ensuring overwrite characteristics and preventing an adverse effect resulting from side erase, such as degradation in an output signal. An exposed surface of a magnetic pole portion layer is configured to have the shape of an asymmetric inverted trapezoid corresponding to a remaining region which remains after removing a width increasing region in the shape of a right triangle from a rectangular region on the side of a side edge. The side edge of the exposed surface is caused to correspond to the side on which a magnetic flux emitted from the magnetic pole portion layer onto a target track of a hard disk causes information to unintentionally overwrite existing information recorded on an adjacent track. This configuration allows preventing the exposed surface from extending to the adjacent track, thus preventing the adverse effect resulting from side erase.