To provide a method for detecting the failure of a servo controller having high failure detecting capabilities by reducing any influence on a post stage system.

A servo controller is provided with a current driver part 3 and a torque motor 21 operating according to a current command, a servo actuator 20 operating according to the output of the torque motor 21, an integrating element 68 interposed between the torque motor 21 and the actuator 20, a position sensor 41a for detecting the displacement of the outputting part of the actuator 20, and a subtractor 61 for subtracting the detection signal of the position sensor 41a from an actuator position command inputted from the outside part and for outputting the subtracted value as a current command. Then, a dummy signal is superimposed on the current command, and the output change of the current driver part 3 and the toque motor 21 is monitored synchronously with the superimposing timing.