To provide a method for detecting rotation angle which attains superior temperature characteristics and detects the rotation angle with high accuracy, using a simple constitution.

When a rotation angle detection object 3 rotates, first, a first galvano-magnetic device 1 detects an impressed magnetic field varying in the form of a sinusoidal wave and a second galvano-magnetic device 2 detects the impressed magnetic field varying, in the form of a cosine wave. Secondly, an output Vy of the second galvano-magnetic device 2 is amplified by an amplification factor of a predetermined ratio by a galvano-magnetic device output amplifying part 8. The amplified output is made Vy'. Subsequently, the square sum of the output Vx and the output Vy' is computed in a square sum computing part 9. Next, the square root computation is performed in a square-root computing section 10. Then, the result of this computation is transmitted to a division operating part 11, and the output Vx of the first galvano-magnetic device 1 is divided by the square root of the square sum. Lastly, the rotation angle is computed in a rotation angle computing part (not shown in Fig.), by using a pseudo-straight portion of the result of computation.