To reduce instability of output fluctuation, asymmetrical fluctuation, Barkhausen noise and the like without incurring the reduction of reproducing output by stabilizing a magnetic domain structure in a free layer of a MR sensor part.

In a magnetoresistive effect type thin film magnetic head provided with a lower magnetic shield, a magnetoresistive effect sensor 61 for reproduction, hard magnetic layers 64 and 65 disposed at both end parts of the sensor opposite to each other and stabilizing the magnetic domain structure of the sensor, an upper magnetic shield, an upper magnetic core for recording and a magnetizing coil for recording operation, the magnetoresistive effect sensor for reproduction has a gradient leaned to the negative side for a magnetic distortion constant from the center part to the both end parts of the sensor. Then the magnetoresistive effect type thin film magnetic head has a magnetic distortion controlling layer 62 for controlling the magnetic distortion constant of the sensor and an underground layer 63 for controlling the magnetic characteristics of the hard magnetic layers between the sensor and the hard magnetic layers.