PURPOSE: To provide an automatic feedback gain adjusting unit capable of determining optimum feedback gain having excellent adaptiveness and giving stable motion in combinations between various kinds of motors for controlling high speed positioning and loads.

CONSTITUTION: The automatic feedback gain adjusting unit 20 is provided with computing means 14, 16 for individually computing a positional deviation and torque command storing means 15, 17 for successively and individually storing the computed results of the means 14, 16, a determining means 18 for comparing the values of plural evaluation functions stored in the means 15 and determining gain reducing the values of the evaluation functions, and a torque oscillation judging means 19 for judging the existence of oscillation corresponding to the determined gain based upon the contents of the means 17. The change of gain is repeated so that the evaluation function value of a positional deviation is reduced within a range free from oscillation and the optimum gain can be finally determined.