PURPOSE: To measure the position, velocity or motion direction of an object having an alternating region with different magnetic conductivity in the motion direction.

CONSTITUTION: The device has a permanent magnet member 12 having an axis 18 crossing the magnetic pole surface 20 facing to a moving object and its motion direction 48. A ferromagnet piece 22 with high permeability is fixed on the surface of a magnet 12 with the same axis and the ferromagnet piece 22 length along the motion direction 48 of the object is larger than the width crossing in the motion direction 48. A pair of magnetic field sensors 24 and 26 are fixed above the ferromagnet piece 22 on both sides of the magnet axis 18 along the motion direction of the object. As the ferromagnet piece 22 distorts the magnetic field of the permanent magnet member 12 in the regions of each of the magnetic field sensors 24 and 26, the magnetic flux line in the regions of each of the magnetic field sensors 24 and 26 is introduced in the direction crossing the motion direction 48 of the object. By this, the magnetic field in the regions of each of the magnetic field sensors 24 and 26 becomes uniform and therefore the positioning of ram of a metal die casting machine becomes very easy and the position, velocity and direction of ram can be measured.