A wavelength-classifying type X-ray diffraction device bombards a sample with characteristic X-rays generated from an X-ray generation source, and detects characteristic X-rays diffracted by the sample using an X-ray detector. The X-ray generation source is composed of several metals of different atomic number, respective metals generating several characteristic X-rays of different wavelengths. An X-ray detector is composed of several pixels for receiving X-rays and outputting pulse signals corresponding to X-ray wavelengths. Pixels are respectively furnished with classification circuits. The classification circuits classify and output pixel output signals based on each of characteristic X-ray wavelengths. X-ray intensity is detected on a per-wavelength basis in individual pixels 12. Measurement data based on different wavelength X-rays are acquired simultaneously in just one measurement. Data of diffracted X-rays of different wavelengths are acquired using the entire region of the receiving surface of a two-dimensional detector.