Provided is a projection system capable of obtaining a sharp contrast without being influenced by an ambient light, the projection system including a projection screen, containing a substrate and a polarized light selective-reflection layer formed on the substrate that diffuse-reflects right-handed circularly polarized light or left-handed circularly polarized light. An image is displayed by reflecting an image light irradiated from a projector on the projection screen. An external light screen is installed at an external light entrance and disposed in a sequence of a linearly polarizing plate and a retardation plate from an external side, and the external light screen circularly polarizes a light in reverse direction to the circularly polarized light diffuse-reflected by the polarized light-selective reflection layer. A transmission axis of the linearly polarizing plate is in a horizontal direction.