When researching and developing wind turbine generator systems, there is a need to predict and evaluate the responses of a wind turbine generator system for various cases of wind conditions. Since it is difficult to carry out such researches by actual wind turbines, a wind turbine simulator is necessary. In this paper, a wind turbine simulator which can anticipate the dynamic performances of the target wind turbines is proposed. This simulator consists of a DC motor which can provide the demanding torque precisely, and has a compact system configuration. Experiments and simulations under natural wind conditions by changing the moments of inertia are executed, and a way of controlling the tip speed ratio to be constant, as well as the responses comparison of changing the P gain of PI controller, are also discussed. These studies verified the usefulness of the simulator.