An opaque area is formed in a sidewall portion of a susceptor by stacking a material that is transparent to flash light and a material that is opaque to the flash light to form the sidewall portion or coating a surface of the opaque material with the transparent material. A top surface of the opaque area in the sidewall portion of the susceptor is designed to have a predetermined positional relationship with a top surface of a substrate; the top surface of the opaque area is set at the same position as that of the top surface of the substrate or higher than the top surface of the substrate by a predetermined height. Thus, obliquely incident flash light is absorbed or irregularly reflected by the opaque quartz portion, surrounding an excavated portion of the susceptor.