A front surface of a semiconductor wafer is momentarily heated by irradiation with a flash of light from flash lamps. An upper radiation thermometer and a high-speed radiation thermometer unit measure a temperature of the front surface of the semiconductor wafer after the irradiation with the flash of light. The temperature data are sequentially accumulated, so that a temperature profile is acquired. An analyzer determines the highest measurement temperature of the semiconductor wafer subjected to the flash irradiation from the temperature profile to calculate a jump distance of the semiconductor wafer from a susceptor, based on the highest measurement temperature. If the calculated jump distance is greater than a predetermined threshold value, there is a high probability that the semiconductor wafer is significantly out of position, so that the transport of the semiconductor wafer to the outside is stopped.