showing evaluation examples of the magnetoresitive head each of which is a picture of the magnetized state of a shielding layer 13 a or 13 b based on the image obtained by using the kerr effect firstly the kerr effect will be explained the kerr effect is a physical phenomenon in which a magnetic body generates magnetorotation polarization plane rotation etc depending on a magnetization direction of a magnetic body by illuminating the magnetic body therefore the magnetized state of the magnetic body can be visually observed by using the kerr effect next an example of the magnetoresistive head evaluated by the method of the present invention will be explained note that the magnetoresistive head to be evaluated is not limited to this example as shown in fig1 the magnetoresistive head 1 has a reproducing head section 2 and a recording head section 3 the reproducing head section 2 includes a magnetoresistance effect reproducing element 4 which is formed between a lower shielding layer 13 a and an upper shielding layer 13 b as an inner layer of a multilayer structure a symbol 6 stands for an air bearing surface which faces a surface of a magnetic storage medium e g magnetic disk in the reproducing head section 2 having the multilayer structure an undercoat film 12 the lower shielding layer 13 a the magnetoresistance effect reproducing element 4 and the upper shielding layer 13 b are layered on a substrate 11 for example the substrate 11 is composed of an insulating material e g al 2 o 3 tic.