PURPOSE: To enable the detection of a correct steering angle immediately after the power supply is turned on in the case of turning the power supply on again in a steering wheel steering angle detecting device for detecting the steering angle of a steering wheel in an automobile.

CONSTITUTION: A steering wheel steering angle detecting device is provided with a steering angle sensor 8 and a steering wheel steering angle computing means 1 which are respectively operated in the power supply 'on' state at the 'on' time of the power source of a vehicle. In this case, a state judging means 3 is provided to hold the power supply 'on' state of the steering angle sensor 8 and steering wheel steering angle computing means 1 when there is the possibility of operating a steering wheel even after the power source of the vehicle is turned off.