A conventional rotation angle detection apparatus for detecting a rotation angle of a detected object includes a magnetism generation section, such as a magnet, and a magnetic flux density detection section, such as a Hall element. One of the magnetism generation section and the magnetic flux density detection section is attached to the detected object. The magnetic flux density detection section detects a magnetism of the magnetism generation section when the detected object rotates, thereby detecting the rotation angle of the detected object. For example, JP-A-2002-206911 discloses a rotation angle detection apparatus that includes a magnet as a magnetism generation section, a magnetic flux density sensor as a magnetic flux density detection section, and a signal processor as a processing section. The signal processor executes a correction operation. The signal processor corrects actual output voltages, which are based on an output signals of the magnetic flux density sensor, on the basis of predetermined values (voltage level) corresponding to predetermined correction points. The predetermined correction points are set at regular intervals.
In cases where the intervals of the correction points are constant, a nonlinearity of the output signal is not improved, and an error in the actual output voltages remains as a linearity error in the rotation angle. JP-A-2007-71889 discloses a correction method that divides a region where an output change rate is large more finely than a region where the output change rate is small. Japanese Patent No. 3,491,577 (corresponding to U.S. Pat. No. 6,498,479) discloses a correction method in which output signals of a magnetism detection element are converted into digital signals, and the digital signal are processed with an arcsine function. However, when an output waveform is unclear, the correction methods disclosed in JP-A-2007-71889 and Japanese Patent No. 3,491,577 cannot be used.