A plate-shaped sample with a cross-section perpendicular to a radial direction of a polycrystalline silicon rod as a principal surface is sampled from a region from a center (r=0) of the polycrystalline silicon rod to R/3. Then, the sample is disposed at a position at which a Bragg reflection from a (111) Miller index plane is detected. In-plane rotation with a rotational angle φ on the sample is performed with a center of the sample as a rotational center such that an X-ray irradiation region defined by a slit performs φ-scanning on the principal surface of the sample to obtain a diffraction chart indicating dependency of a Bragg reflection intensity from the (111) Miller index plane on a rotational angle of the sample. A ratio (Sp/St) between an area Sp of a peak part appearing in the diffraction chart and a total area St of the diffraction chart is calculated.