An apparatus for detecting a rotation of, for example, an automotive steering wheel has comprises a rotary plate fixed to a shaft and rotatable in accordance with a rotation of the steering wheel, an electric circuit for detecting a rotation of the rotary plate; a rotary member rotatable in accordance with a rotation of the shaft; a first opening for detecting a reference position signal provided in the rotary plate, a second opening for detecting a reference position signal provided in the rotary member, a reduction gear mechanism for reducing the rotational speed of the rotary member such as to allow the first and second signal detecting openings to be aligned with each other once in a plurality of rotations of the shaft, and photo electro transducers for detecting a reference position disposed in a line passing through the first and second signal detecting openings. The position detecting transducers outputting reference position signal upon an alignment of the first and second signal detecting openings with the line.