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.