To obtain an impact sensor which excludes an influence on a sensor characteristic due to an irregularity in the characteristic of a magnet by a method wherein a bias magnetic field is applied to a magnetoresistance element by using a coil, the bias magnetic field to the magnetoresistance element is changed by a magnetic fluid and a prescribed signal processing operation is executed to the output of the magnetoresistance element by an output circuit part.

An impact sensor 20 is constituted of an MR element (magnetoresistance element) 22 which is installed inside a case 21, of a waveform shaping circuit part (output circuit part) 23 which waveform-shapes the output of the MR element 22, of a coil 24 which applies a bias magnetic field to the MR element 22 and of a magnetic fluid 25. The magnetic fluid 25 is attracted on a magnetic curve which is formed by the coil 24, and it is gathered in the central part of a container 26. Then, when an impact which surpasses the magnetic attractive force of the coil 24 used to gather the magnetic fluid 25 is applied from one direction going around by 360° in the Y-direction and the Z-direction, the magnetic fluid 25 is moved, the intensity of the magnetic field applied to the MR element 22 is changed, and a change in an output voltage is obtained.