To provide a servo actuator control device capable of continuously disconnect a servo control valve 39 in abnormal condition with the switching operation obstructed from a control system certainly and allowing the servo control valve 39 to make service for the control operation when its restitution is made from the abnormal condition to the normal condition.

In the normally operating condition in which a projection 63 on a coupling arm 59 is inserted in a recess 58, the swinging of a fourth link 46 based upon the resultant force of the operational input and the feedback input is transmitted through a crank body 49 to the servo control valve 39, and the servo actuator 31 according to the invention is put under servo control. In the abnormal condition in which the servo control valve 39 can not be switched owing to sticking, etc., the projection 63 on the arm 59 will slip off from the recess 58, so that the swinging of the fourth link 46 based upon the resultant force is absorbed on the way and shut off, and the servo control valve 39, etc., is disconnected from the whole control system.