PURPOSE: To make multipoint measurements of steering angle in the span direction of the rudder of the aileron, etc., of an aircraft by photographing the outside diameter of the rudder with a camera, and processing the taken images for measurement of the steering angle.

CONSTITUTION: To measure the steering angle of an aileron 3 provided on, e.g., the main wing 2 of an aircraft 1, a television camera 7 is mounted on the base part of the vertical tail 6 of the aircraft 1 via a transparent window frame. A plurality of gauge marks 8 for steering angle measurements are painted on the aileron using a paint which allows a clear distinction from peripheral portions. Images taken with the television camera 7 are input to a gauge mark signal separation device 10 via an image processing device 9. Thereafter, a steering angle signal δ1, at the required gauge mark Ai is processed by a recording device, a transmitting device, and an electrical signal converting device or the like which are not shown in the figure, to measure the steering angle. Thereby multi-point measurements of the steering angle can be made in the span direction of a rudder.