According to a method of manufacturing a thin film magnetic head, a magnetoresistive device and an alumina layer are formed on a substrate, then the alumina layer is covered with a covering layer made of metal such as Ti having a thickness of more than 10 nm, then a photoresist film is formed on the covering layer, and then an opening is formed by exposing and developing the photoresist film. In turn, a magnetic metal film is formed on an allover surface, then the photoresist film and the magnetic metal film thereon are removed. The thin film magnetic head structured as above may provide a good magnetic characteristic since it has the covering layer on the alumina layer to prevent the alumina layer from being corroded by liquid developer. In addition, a magnetic recording unit employing the thin film magnetic head may reproduce data recorded with high density.