The upper magnetic pole layer andor lower magnetic pole layer comprises a soft magnetic film having a variable region in which the chemical composition of Fe changes in the direction of thickness in at least a part thereof, and the difference of the proportions of Fe between the regions most abundant in Fe and most deficient in Fe is 4% by mass or more in the variable region. Sub-matrices and entries outside the sub-matrices in a first band matrix are identified. The elastic seal member is arranged so that a hollow cylinder is compressed in a direction of an axis of the hollow cylinder.