The intrinsic properties of an ultrasonic motor (high torque for low speed, high static torque, compact in size, no electromagnetic interference, etc.) offer great advantages for industrial applications. However, when load torque is applied, a dead-zone occurs in control input. Therefore, a sliding-mode controller, which is a non-linear controller, is adopted for the ultrasonic motor. The state quantities, such as acceleration, speed, and position, are needed to apply the sliding-mode controller for position control. However, a rotary encoder causes quantization errors in the speed information. This article presents a robust position control method for an ultrasonic motor by using a variable structure system observer. The state variables for the sliding-mode controller are estimated by the variable structure system observer. A small, low-cost, and good response sliding-mode controller is designed in this work by using a microcomputer that is essential in an embedded system for the development of industrial equipment. The effectiveness of the proposed method is verified by experimental results.