To provide a servo valve which can move a spool to a given position by air pressure irrespective of a gravitational direction even at the time of power failure and can make an actuator operate at a safety side for actuator positioning.

There is provided a servo valve 100 equipped with a spool 10 having first and second valve bodies 11, 12, and a sleeve 20 which houses the spool movably in an axial direction and has an air feeding port 30 for feeding air to a portion between the first and second valve bodies. In the servo valve, the first and second valve bodies 11, 12 have pressure receiving surfaces 11a, 12a for receiving air pressure caused by air from the feeding port. Then, an area of the pressure receiving surface of the first valve body is formed larger than that of the second valve body, while the spool moves to a direction of the first valve body by feeding the air.