A semiconductor wafer with (100) plane orientation has two orthogonal cleavage directions. A notch is provided so as to indicate one of these directions. During irradiation with a flash, the semiconductor wafer warps about one of two radii at an angle of 45 degrees with respect to the cleavage directions such that the upper surface thereof becomes convex, and the opposite ends of the other radii become the lowest position. Eight support pins in total are provided in upright position on the upper surface of a holding plate of a susceptor while being spaced at intervals of 45 degrees along the same circumference. The semiconductor wafer is placed on the susceptor such that any of the support pins supports a radius at an angle of 45 degrees with respect to a cleavage direction.