A rotation angle detecting device includes a magnetic field forming member, magneto-sensing IC circuit including first and second sensing sections in a magnetic field to have a first preset angle between them, and a selecting circuit. One of the first and second sensing section includes plural magneto-sensing elements whose sensing surfaces face in directions different from one another by a second preset angle. When the magnetic field forming member rotates relative to the magneto-sensing means, the magneto-sensing elements respectively provide the output signals. The selecting circuit selects a pair of the output signals of the magneto-sensing elements that is closest to a preset phase difference angle.