Provided are a method and an apparatus of precisely measuring the intensity profile of an x-ray nanobeam, which can measure x-rays having different wavelengths with one knife edge and can perform optimal measurements corresponding to the depth of focus of an x-ray beam and the conditions of other measurement devices, using a dark field measurement method which enables precise measurements of the profile of an x-ray beam using a knife edge and using diffracted and transmitted x-rays. The knife edge (4) is formed of a heavy metal which advances the phase of an x-ray passing therethrough and is fabricated in such a manner that the thickness may change in the longitudinal direction continuously or in a stepwise fashion. The knife edge (4) is so set that an x-ray beam may traverse the knife edge (4) at such a thickness position as to achieve a phase shift in a range wherein a transmitted x-ray and a diffracted x-ray diffracted at the end of the knife edge may reinforce each other, and a superposed x-ray of the diffracted x-ray and the transmitted x-ray is measured by an x-ray detector.