Making thinner the magnetic domain control layer deteriorates the magnetic properties. Also, disturbances tend to increase the magnetization dispersion of the magnetic domain control layer, thereby lowering the magnetic domain control bias magnetic field. In one embodiment of the invention, a first magnetic domain control layer is provided in the proximity of the free layer of the GMR sensor in such a way that the track width is Twr1. Outside the first magnetic domain control layer is provided a second magnetic domain control layer. The second magnetic domain control layer placed outside the first magnetic domain control layer gives the first magnetic domain control layer an external bias field. The amount of magnetization of the tip of the first magnetic domain control layer is polarized and increased by the bias magnetic field from the second magnetic domain control layer. This causes the first magnetic domain control layer to apply a strong bias magnetic field having a lower dispersion to the free layer of the GMR sensor.