A rapid thermal processing apparatus comprises a processing chamber which subjects a semiconductor substrate to rapid thermal processing. A substrate support part is arranged in the processing chamber and supports the substrate. A lamp part optically irradiates the substrate supported by the substrate support part and heats the substrate. A thermo sensor is provided to measure a temperature of the substrate. A temperature computing part computes the temperature of the substrate based on an output signal of the thermo sensor. A control part controls an irradiation intensity of the lamp part according to the temperature computed by the temperature computing part. In this apparatus, the control part is provided to correct a control parameter of the irradiation intensity of the lamp part based on a measured reflectivity of a surface of the substrate.