In this paper, nonlinear dynamic response of a traveling wave type ultrasonic motor is investigated. In particular, understanding the transient dynamics of a bar-type ultrasonic motor, such as starting- up and stopping, is of primary interest. First, the transient response of the bar-type ultrasonic motor at starting-up and stopping was measured using Laser Doppler Velocimeter (LDV), and its driving characteristics are discussed in detail. The motor is shown to possess amplitude-dependent nonlinearity that greatly influences the transient dynamics of the motor. Second, a dynamical model of the motor is constructed as a second-order nonlinear oscillator, which represents the dynamics of piezoelectric ceramics, stator, and rotor. The model features nonlinearities caused by the frictional interface between the stator and the rotor, and cubic nonlinearity in the dynamics of the stator. Coulomb's friction model is employed for the interface model and stick-slip phenomenon is considered. Lastly, it is shown that the model is capable of representing the transient dynamics of the motor accurately. The critical parameters in the model are identified from measured results, and numerical simulations are conducted using the model with the identified parameters. Good agreement between the results of measurements and numerical simulations is observed.