A screen device in which a screen is stretched in such a manner as to be capable of being freely opened and closed, comprising: a screen frame that is installable in a building opening; an operating stile that is vertically disposed in the screen frame and is capable of being operated to move side to side; the screen that is stretched between one of left and right vertical-frame poles (2a, 2b) of the screen frame and the operating stile and that opens and closes the screen frame as a result of the operating stile being operated and moved; a screen guide (15, 15A, 15B) that is provided at at least one of upper and lower ends of the screen and that is drawn out from the inside of the operating stile along an end portion of the screen and is drawn into the inside of the operating stile as a result of the operating stile being operated and moved; and a support rail that linearly supports, along the screen, the screen guide (15, 15A, 15B) that is drawn out from the inside of the operating stile, wherein the support rail includes a first engagement edge and a second engagement edge that protrude in a widthwise direction of the support rail in such a manner as to face away from each other, wherein the screen guide (15, 15A, 15B) is formed by connecting a plurality of guide pieces (17, 17A, 17B) to one another in series such that the screen guide (15, 15A, 15B) is capable of being bent only in one direction, characterized in that each of the guide pieces (17, 17A, 17B) includes a piece body that engages the end portion of the screen and an engagement member including a first engagement portion and a second engagement portion that engage the first engagement edge and the second engagement edge of the support rail, respectively, and wherein the engagement member is coupled to the piece body in such a manner as to be capable of being displaced to a first position at which the first engagement portion and the second engagement portion engage the first engagement edge and the second engagement edge of the support rail, respectively, and to a second position at which the first engagement portion and the second engagement portion are respectively detached from the first engagement edge and the second engagement edge. a screen frame that is installable in a building opening; an operating stile that is vertically disposed in the screen frame and is capable of being operated to move side to side; the screen that is stretched between one of left and right vertical-frame poles (2a, 2b) of the screen frame and the operating stile and that opens and closes the screen frame as a result of the operating stile being operated and moved; a screen guide (15, 15A, 15B) that is provided at at least one of upper and lower ends of the screen and that is drawn out from the inside of the operating stile along an end portion of the screen and is drawn into the inside of the operating stile as a result of the operating stile being operated and moved; and a support rail that linearly supports, along the screen, the screen guide (15, 15A, 15B) that is drawn out from the inside of the operating stile, wherein the support rail includes a first engagement edge and a second engagement edge that protrude in a widthwise direction of the support rail in such a manner as to face away from each other, wherein the screen guide (15, 15A, 15B) is formed by connecting a plurality of guide pieces (17, 17A, 17B) to one another in series such that the screen guide (15, 15A, 15B) is capable of being bent only in one direction, characterized in that each of the guide pieces (17, 17A, 17B) includes a piece body that engages the end portion of the screen and an engagement member including a first engagement portion and a second engagement portion that engage the first engagement edge and the second engagement edge of the support rail, respectively, and wherein the engagement member is coupled to the piece body in such a manner as to be capable of being displaced to a first position at which the first engagement portion and the second engagement portion engage the first engagement edge and the second engagement edge of the support rail, respectively, and to a second position at which the first engagement portion and the second engagement portion are respectively detached from the first engagement edge and the second engagement edge.