A transmission type small-angle scattering device of the present invention includes a goniometer 10 including a rotation arm 11. The rotation arm 11 is freely turnable around a θ-axis extending in a horizontal direction from an origin with a vertical arrangement state of the rotation arm being defined as the origin, and has a vertical arrangement structure in which an X-ray irradiation unit 20 is installed on a lower-side end portion of the rotation arm 11, and a two-dimensional X-ray detector 30 is installed on an upper-side end portion of the rotation arm 11 to form a vertical arrangement structure.