Described herein is an X-ray beam conditioning device that has a crystal holder and a motor. The crystal holder supports a first crystal block and a second crystal block, each of which diffracts X-ray by a specific diffraction angle. The motor can rotate the crystal holder around an axis extending at right angles to a plane including an optical axis of X-ray and can support the crystal holder and fixedly supporting the crystal holder at thus rotated position. The crystal holder holds the first and second crystal blocks at such angles to each other that both crystal blocks diffract X-ray. The optical axes of the two crystal blocks can be adjusted, merely by rotating the crystal holder about said axis, namely only one axis.