An ultra-small angle X-ray scattering measuring apparatus comprising: a sample support device for supporting a sample; an X-ray generation device for taking out X-rays radiated from an X-ray real focus with a predetermined focus size and emitting them toward the sample; an X-ray detection device for detecting X-rays emitted from the sample; a monochromator arranged between the X-ray real focus and the sample support device; and an analyzer arranged between the sample support device and the X-ray detection device, wherein the monochromator and the analyzer each have a pair of oppositely disposed X-ray reflection surfaces and are formed of a perfect crystal; the analyzer being driven to rotate for scanning around a 2θ-axial line(2θ) orthogonal relative to an X-ray optical axis running through the analyzer, and the X-ray detection device being configured to detect X-rays at every angular position within the scanning rotation of the analyzer, both said monochromator and said analyzer collimate x-rays in the plane perpendicular to said 2θ-axial line; and characterised in that: the apparatus further comprises an X-ray collimating mirror arranged between the X-ray real focus and the monochromator, said X-ray collimating mirror including a first mirror and a second mirror arranged orthogonally relative to each other, the first mirror and the second mirror each having a multilayer film formed by alternately laying layers of a heavy element and layers of a light element so as to operate as an X-ray reflection surface; the multilayer film has a profile of a paraboloid, and is comprised of lattice planes having an interplanar spacing(d), the interplanar spacing(d) of the lattice planes of the multilayer film being made to continuously change along the paraboloid so as to satisfy the Bragg's condition for diffraction at any arbitrarily selected position on the X-ray reflection surface relative to X-rays of a specific wavelength; and the first mirror and the second mirror are inclined respectively relative to a plane which includes the X-ray optical axis and is orthogonal to the 2θ-axial line(2θ) by an angle of 45 degrees. a sample support device for supporting a sample; an X-ray generation device for taking out X-rays radiated from an X-ray real focus with a predetermined focus size and emitting them toward the sample; an X-ray detection device for detecting X-rays emitted from the sample; a monochromator arranged between the X-ray real focus and the sample support device; and an analyzer arranged between the sample support device and the X-ray detection device, the apparatus further comprises an X-ray collimating mirror arranged between the X-ray real focus and the monochromator, said X-ray collimating mirror including a first mirror and a second mirror arranged orthogonally relative to each other, the first mirror and the second mirror each having a multilayer film formed by alternately laying layers of a heavy element and layers of a light element so as to operate as an X-ray reflection surface; the multilayer film has a profile of a paraboloid, and is comprised of lattice planes having an interplanar spacing(d), the interplanar spacing(d) of the lattice planes of the multilayer film being made to continuously change along the paraboloid so as to satisfy the Bragg's condition for diffraction at any arbitrarily selected position on the X-ray reflection surface relative to X-rays of a specific wavelength; and the first mirror and the second mirror are inclined respectively relative to a plane which includes the X-ray optical axis and is orthogonal to the 2θ-axial line(2θ) by an angle of 45 degrees.