In a projector, green CRT projection tubes for displaying pictures for the right and left eyes are arranged on the right and left sides with respect to a screen respectively, while a red CRT projection tube for convergence adjustment is arranged at the center. Further, the projector includes polarizing filters which are provided on respective front surfaces of the CRT projection tubes, a triple two-input one-output type selector switch, and a convergence adjusting picture signal source. In general, a right eye picture signal from a right eye picture signal source is supplied to the CRT projection tube through the selector switch, while a left eye picture signal from a left eye picture signal source is supplied to the CRT projection tube through the selector switch. At this time, the observer can visually recognize a stereoscopic monochromatic picture through polarizing glasses. In convergence adjustment, the convergence adjusting picture signal source generates a picture signal of a convergence adjustment image which is supplied to the projection tubes via the selector switch.