Patent ID: 7078893

Claim:
A rotation angle detecting device comprising: a magnet that rotates with a rotation of an object to be measured, the magnet including two ends magnetized so as to have opposite polarities; a magnetic substance unit forming a predetermined air gap with the two ends of the magnet, the magnetic substance unit being divided into magnetic members so as to provide plane symmetry with respect to a vertical plane perpendicularly crossing a rotational center axis of the magnet to form a magnetic detection gap by the division; and a non-contact magnetic detection element provided in the magnetic detection gap between the magnetic members so as to output a signal corresponding to a density of a magnetic flux passing through the magnetic detection gap, wherein a rotation angle of the object to be measured is detected based on the output signal from the magnetic detection element, and the magnetic members each include a reverse warp part so that the air gap suddenly increases when the magnet rotates at a predetermined rotation angle from a state where the air gap is minimum in a direction in which the air gap increases.