There is provided an electromechanical machine control system for variable speed controlling an electromechanical machine which can realize a desired control response and a stable control system by online regulating the gain of a linear differential controller by current feedback based on an electric parameter or mechanical parameter of the electromechanical machine. The electromechanical machine control system includes a current coordinate transformer (15) for coordinate transforming a current detection value of the electromechanical machine (13) which is inputted into a γ-axis current having the same phase as a position reference and a δ-axis current which advances 90 degrees further than the position reference, a δ-axis stabilizer (16) for implementing a linear differential control on the δ-axis current which is inputted to output a δ-axis current voltage correction amount and a δ-axis stabilizing gain regulator (17) for regulating the linear differential control gain of the δ-axis stabilizer.