PURPOSE: To provide the servo control unit which can greatly reduce position deviation by speedily and automatically adjusting the gain of feedforward.

CONSTITUTION: When a position command θr, a speed command ωr, and an acceleration command ω'r are outputted from a command value generating device 1, a control system operates according to the commands to drive a machine to be controlled. At this time, a feedforward gain error estimation part 11 operates to estimates gain errors of feedforward, i.e., a torque feedforward gain error Δj and a speed forward gain error ΔKVFF from the speed command ωr and acceleration command ω' and the position deviation corresponding to them and output the estimated position to a feedforward control part 8A. This feedforward control part 8A adjusts the feedforward gain of the control system on the basis of the gain errors estimated by the gain error estimation part 11 so that the position deviation θr-θ becomes zero.