An exposure device of a color copying apparatus has a filter holding frame mounting a filter plate provided with color filter layers and a transparent section and a pair of aperture plates for forming a variable aperture. The filter holding frame is movable in one direction perpendicular to an exposure light path to selectively place the filter layer and transparent section into the exposure light path. The aperture plates are movable close to and away from each other in a direction perpendicular to the one direction and the exposure light path so as to vary the size of aperture formed thereby. Between the filter holding frame and the pair of aperture plates there is a mechanism comprising pins and cam grooves for cooperating the filter holding frame and the aperture plates. The cam groove comprises a straight cam section which is provied to place the pair of aperture blades out of the optical path so as to maintain the maximum size of the variable aperture and extends in a direction in parallel with the direction in which the filter holding frame moves and an inclined cam section which is provided to bring the pair of the aperture blades into the optical path so as to vary the size of the variable aperture and inclined at an angle with respect to the straight cam section.
