The present invention provides a tire testing machine, including a mantrel member rotatably holding the tire being in an inflatable state at a presetting inner pressure, and a drum member for transferring a running force to the tire by contacting the drum to an outer circumferential surface of the tire held by the mantrel member. The tire testing machine also includes a detector arranged on the mantrel member for measuring a load of the tire, wherein the detector is fixed on the mantrel member by passing a prestress bolt through a mounting hole arranged on the center of the detector, a coolant passage formed by hollowing a corresponding portion passing the mounting hole of the detector is arranged in the prestress bolt, and a coolant can thus be supplied to the coolant passage.