A rotation angle detecting device comprises a first rotation detecting unit (50) and a second rotation detecting unit (72), that are for detecting continuously a rotation angle of a measurable rotation body (S) with different cycles between each other, wherein the individual rotation detecting units are provided for increasing and decreasing individual output signals, that are obtained in response to a rotation of the measurable rotation body, in a same direction corresponding to a rotational direction of the measurable rotation body, a difference is evaluated for between the individual output signals obtained from the first rotation detecting unit and from the second rotation detecting unit in response to the rotation of the measurable rotation body, and the output difference is used for a detection of an absolute rotation angle within a detectable rotation angle defined by a least common multiple of a cycle of a first output signal obtained from the first rotation detecting unit and a cycle of a second output signal obtained from the second rotation detecting unit. As a result, there is provided the rotation angle detecting device, for designing to reduce the number of components to comprise the rotation angle detecting device, for achieving a reduction in size regarding the rotation angle detecting device itself, and for becoming possible to detect a rotation angle in highly accurate.