Even a radiation thermometer using a quantum infrared sensor appropriately measures the temperature of a substrate irradiated with a flash of light. A heat treatment apparatus includes a quantum infrared sensor configured to measure a temperature of the first substrate and a temperature of the second substrate. The heat treatment apparatus further includes a temperature correction unit configured to correct, using a correction coefficient calculated based on the reference temperature and the shift temperature, a temperature of the second substrate on which second heat treatment having irradiation with the flash of light is performed, the temperature being measured by the quantum infrared sensor.