Abstract: An apparatus for turning the posture of flat articles (such as envelopes and post cards) can stably clamp and turn a flat article accurately, with a 90.degree. rotation. The turning apparatus has a cone roller that is disposed along a path for transporting the flat articles. A first plurality of idler pulleys are independently mounted to engage and be driven by the conical surface of the roller. A second plurality of idler pulleys are disposed on the upstream side of the conical surface, with respect to the first idler pulley. At least one running belt is stretched between the first and second idler pulleys. The angle between the conical surface and the running belt is small enough to reliably grip and turn the flat article.