The present invention provides a thin film magnetic head capable of satisfying both assurance of recording performance and assurance of reproduction performance. In the case where a lower magnetic layer is formed of an iron cobalt alloy (for example, Fe.sub.65Co.sub.35) which contains iron in a range of 60 at % to 80 at % and has extremely high saturation magnetic flux density of 2.4 T or higher, a head isolation layer formed of ruthenium (Ru) is provided between the lower magnetic layer and an upper read shield layer portion. As compared with the case where the head isolation layer is not provided between the lower magnetic layer and the upper read shield layer portion, the strength of a recording magnetic field increases and a reproduction output of an MR element is stabilized.