a screen device in which a screen is provided in a contractable and expandable manner between a pair of screen installation frames , at least one of which is movable in a sliding manner , and the screen can be opened and closed by pulling it sideways , and which has upper guide frames for guiding the screen installation frames while covering their upper end sections . the screen installation frames have , at their upper end sections , fall - down prevention guide sections . the upper guide frames have , in their insides , guide rail projections which prevent , by holding the fall - down prevention guide sections , the upper end sections of the screen installation frames from coming out of the upper guide frames .