A thin film magnetic head having a high write-in accuracy can be produced by suppressing a magnetic field leak between upper and lower magnetic poles. The method of producing the thin film magnetic head, in which a head substrate, magnetoresistance effect element, lower magnetic pole, write gap layer and an upper magnetic pole are formed in this order, has the lower magnetic pole patterned with a larger width than that of the upper magnetic pole in a write magnetic pole after the lower magnetic pole is formed. An insulation layer is formed in the same layer as the lower magnetic pole such that the insulation layer is flattened with the lower magnetic pole. The upper magnetic pole is formed on a surface of the write gap layer after the write gap layer is formed, and a protrusion of the lower magnetic pole is removed from a side face thereof.