Abstract: The present invention provides an adaptive sliding mode control method capable of not only improving the convergence of estimated parameters but also providing outstanding vibration-damping properties. In this method, a position deviation .epsilon. between a command position and a motor position, a speed deviation .epsilon., and a position command acceleration .theta.r are determined. The difference .epsilon.t between the motor position and the position of machine's moving part and a differential .epsilon.t based thereon are obtained by observer processing and filtering processing. A phase plane Suf of the motor is obtained by feeding back the deviation .epsilon.t between the motor position and the position of the machine's moving part. Estimated values Jhat, Ahat and Grhat, representing an inertia term, coefficient of dynamic friction, and gravity term respectively, are obtained. A switching input .tau.