A valve is configured to control an opening in a passage. A valve angle sensor is configured to send an electric signal according to a rotation angle of the valve. In a storing process, an actual measurement value of a valve angle at a mechanical full open position is stored as an actual full open valve angle. In a first setting process, a first output value at a mechanical full close position is set. In a second setting process, a second output value at the stored actual full open valve angle is set. The output characteristic is set as an angle to output value relation according to the first output value and the second output value.