To provide an electro-pneumatic transducer which is safe even in the case of a power failure and never raises the cost of wiring.

A comparison arithmetic part 34 compares an input electric signal 36 and a feedback signal obtained by converting an output air pressure signal 29 into an electric signal through a pressure sensor 33 and inputs their comparison difference value to an solenoid valve control part 35. The solenoid valve control part 35 supplies a solenoid valve control signal to a solenoid valve 25 or 27 according to the inputted difference value to open the solenoid valve 25 or 27. Supply air pressure 21 is released from a nozzle 26 or 28 through the solenoid valve 25 or 27 which is opened. Consequently, a windmill 32 rotates and its rotational force is transmitted to a cam 30 through a speed reducing mechanism 31. The cam 30 is rotated to increase or decrease the blocking area of the opening part of a nozzle 24. As the blocking area of the opening part varies, the back pressure of the nozzle 24 also varies.