PURPOSE: To easily perform zero-span adjusting in an electropneumatic positioner which controls an opening of an adjusting valve corresponding to an input signal.

CONSTITUTION: A position sensor 2 detects a lifting position corresponding to an opening of an adjusting valve 1. A control part 4 generates a control signal corresponding to an input signal and a detection signal of the position sensor 2. An electropneumatic converter 5 generates a pneumatic pressure signal corresponding to the control signal and feeds it to the adjusting valve 1. A pressure sensor 6 detects a pressure value from the pneumatic pressure signal and feeds it to the control part 4. The control part 4 compares the detection value of the pressure sensor 6 which is varied by gradually varying the control signal with lower/upper limit values of the preset pneumatic pressure. The lifting position which corresponds to the valve opening when the detection value is the lower limit value is treated as a zero point. The lifting position which corresponds the valve opening when the detection value is upper limit value is treated as span.