A projection display device having a plurality of transmission screens, each having an image display portion of different dimension, and each having light transmissivity and being provided with a back surface layer having optical directivity on a back surface side; a main body capable of projecting a projection light, and a optical unit that guides the projection light from the projection device main body to the back surface of the transmission screen; and a supporting unit that supports one transmission screen selected from the plural transmission screens and the projection device main body. An image is displayed on the transmission screen by allowing the projection light guided by the optical unit to pass through from the back surface side. One transmission screen is selected, and the selected transmission screen, the projection device main body, the optical unit, and the supporting unit are assembled for use.