To provide a steering angle sensor which can detect a steering angle nearly simultaneously with the turning-on of an IG key without continuously detecting steering angle information when the IG key is turned off.

The steering angle sensor is provided with a ring belt-shaped magnet 23 which is attached through a yoke 22 to the output shaft 21 of a gear mechanism used to convert the whole rotation-angle range of a steering shaft into a rotation-angle range at less than one rotation in both directions and which is magnetized in the radial direction; stators 24 which are fixed to, and arranged at, the outer circumference of the ring belt-shaped magnet at an interval of 90° by keeping prescribed gaps 25; and magnetic sensors 26, 27 which are installed at two adjacent gaps from among the four gaps. One from among the two magnetic sensors is used to judge regions at an interval of 90°, and the other is used to acquire an angle signal.