A tire traveling test device has a belt that horizontally spans between two drums and a load support device that supports a flat surface of the belt from a lower surface side of the belt. The load support device is provided with a liquid supply means that supplies support liquid between the load support device and the belt and supports the belt from below. The liquid supply means is provided with a plurality of supply holes from which support liquid can be discharged between the load support device and the belt. Additionally, the liquid supply means can adjust the flow rate of the support liquid discharged from the supply holes on the basis of the fluid pressure, which changes according to the tire contact state.