A rotation angle detection device that is capable of detecting an absolute rotation position with a high accuracy without an error. A rotation detection target rotates together an operatable rotation member and has an outer scale and an inner scale. Two rotation detection elements are arranged at opposite positions across the rotation axis in the radial direction so as to respectively irradiate the outer and the inner scales with light beams and output signals corresponding to reflected components. A control unit calculates a rotation angle of the rotation detection target using the signals. The outer and inner scales are so formed that a signal output from one of the two rotation detection elements increases and the signal output from the other decreases when the rotation member is rotated.