The spiral rotary member includes a main body section, a fin section that is disposed on an outer peripheral surface of the main body section and spirally arranged around a longitudinal axis C and an X-ray cutoff section that cuts off X-rays. The X-ray cutoff section is arranged so that a clear region to be clearly imaged by an X-ray and an unclear region to be unclearly imaged by X-rays are distinguished under X-ray observation in a periaxial direction of the longitudinal axis of the spiral rotary member, the X-ray cutoff sections being further arranged on the same straight line along a longitudinal axis direction of the spiral rotary member or the X-ray cutoff section being further arranged in the form of a band.
