To provide a rotation angle detecting device capable of achieving a detection of the angle of rotation at a high speed and with high accuracy and a bearing assembly utilizing such rotation angle detecting device, the rotation angle detecting device includes a magnetic generator (4) arranged on a rotatable member (1) and a plurality of linear magnetic sensor arrays (5A to 5D) arranged on a stationary member (2), so that a zero-crossing-position in a distribution of magnetic field can be detected from respective outputs of the magnetic sensor arrays (5A to 5D) and the rotation angle of the magnetic generator (4) can be detected from the detected zero-crossing-position. While based on the previous zero-crossing-position, the subsequent scanning range of the magnetic sensor arrays (5A to 5D) is set, the zero-crossing-position is detected within this limited scanning range.