We have proposed a volumetric 3D display in which cross-sectional images are projected on a rotating spiral screen. One of challenges of this method is an existence of a blind area generated depending on viewpoints. In this research, a new type of screen was fabricated to reduce the blind spot area by trimming off as much of the screen as possible except for the spiral surface. The blind spot area was calculated by ray tracing simulation and compared with that of the screen without the trimmed spiral surface. As a result, the visibility of the left semicircular region was improved when the viewpoint position of the new screen was low.