PURPOSE: To improve the reliability of each product and to reduce the load of adjusting work required at the time of shipping the product by automatically adjusting the control characteristics of a DC servo motor control system to an optimum state at the time of executing the control system.

CONSTITUTION: Prior to the start of control operation of a motor 1, a feedback loop from an encoder 2 to a DC servo motor control part 3 is disconnected and a control signal for impressing step voltage to the motor 1 is sent to the control part 3 to start the rotation of the motor 1. A change in the rotational speed of the motor 1 is detected by a signal outputted from the encoder 2, a transient response characteristic from the change of the rotational speed is analyzed and a control parameter optimum to the control of the motor 1 is selected from a previously prepared control parameter table and set up in a DC servo motor control part 3. Then the feedback loop is restored and normal control is started by control characteristics based upon the control parameter set up in the control part 3.