A rotation angle detection apparatus includes a driving gear, two driven gears, two sensors, and an arithmetic circuit. The two driven gears have different numbers of teeth and each are in mesh with the driving gear. The arithmetic circuit is configured to compute a rotation angle of the driving gear based on the rotation angles of the two driven gears, detected through the two sensors. The arithmetic circuit is configured to, when a relationship between the rotation angles of the two driven gears, detected through the two sensors, is different from the relationship when the rotation angle of the driving gear, computed by the arithmetic circuit, is normal, detect an abnormality in the rotation angle of the driving gear, computed by the arithmetic circuit.