Provided is an optical axis adjustment device for an X-ray analyzer comprising an incident-side arm, a receiving-side arm, an X-ray source, an incident-side slit, and an X-ray detector, wherein the device comprises a shielding strip disposed at a position blocking X-rays received by the X-ray detector from the X-ray source, and a shielding strip-moving device that rotates the shielding strip around the sample axis relative to the optical axis of X-rays reaching the X-ray detector from the X-ray source to two angle positions, and the amount of deviation in parallelism of the surface of a sample with respect to the optical axis of the X-rays is found on the basis of X-ray intensity values found by the X-ray detector for the two angle positions.