A fatigue limit stress specification system includes: a vibration generator that repeatedly applies a load to an object to be measured; a temperature sensor that measures a change in temperature of the object to be measured; and an information processing device that measures a fatigue limit stress of the object to be measured. The information processing device obtains a relation between a temperature amplitude of a fundamental frequency component of vibration for the object to be measured and a temperature amplitude of a second harmonic component of the vibration, performs fitting on the relation by using a first approximate line and a second approximate line, the first approximate line including a quadratic curve, the second approximate line including a quadratic curve, and obtains the fatigue limit stress of the object to be measured based on an intersection of the first approximate line and the second approximate line.