To provide a low-cost range determination device high in detection accuracy; and its manufacturing method.

This range determination device is provided with: polarity sensors 26 (26a-26c); first magnets 24 relatively movably arranged with respect to the polarity sensors 26 in response to selection of the range of an automatic transmission, wherein polarity thereof is reversed at least at one position in the relative movement direction; a range determination means determining the range based on a detection signal of the polarity of the first magnet 24 detected by the polarity sensor 24 in response to the relative movement; and magnetic bodies 25 each arranged at a position increasing magnetic flux density in the vicinity of the boundary of the first magnet with the polarity reversed in the relative movement direction. Since the variation gradient of the magnetic flux density in the vicinity of the boundary is increased, it is not necessary to use an expensive magnet having large magnetic flux density as a first magnet 24, and the detection accuracy of the range determination device 14 can be improved at low cost.