A laser beam from a laser optical system is incident onto a semiconductor wafer. Thermal radiation light from the semiconductor wafer is incident onto an infrared detector. The infrared detector outputs a signal based on the intensity of the thermal radiation light. A processing device calculates a sheet resistance of the semiconductor wafer that is annealed by the laser beam on the basis of an output value of the infrared detector, and outputs a calculation value of the sheet resistance to an output device.