To prevent detection output from depending on the concavo-convex pitch of a magnetic material mobile unit by using at least a pair of magnetic field vector detection type spin-valve type huge magnetic resistance elements as a magnetosensitive element, and arranging the magnetic field vector detection type spin-valve type huge magnetic resistance elements so that pin layer magnetization directions of the pair of spin-valve type huge magnetic resistance elements face an abbreviation forward direction and an abbreviation opposite direction to the moving direction of the magnetic material mobile unit respectively.

This mobile unit detection device is provided with a gear 1 as the magnetic material mobile unit having at least a convex or concave part, a bias magnet 5 for applying bias magnetic field thereto, and two pairs of spin-valve type huge magnetic resistance elements R1, R2 and R3, R4. The magnetic field vector detection type spin-valve type huge magnetic resistance elements are linearly-arranged so that the pin layer magnetization directions of the pair of spin-valve type huge magnetic resistance elements face the abbreviation forward direction and the abbreviation opposite direction to the moving direction of the gear 1 respectively.

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