Projector comprising a housing, a support frame formed with a carrying surface for carrying a flexible file sheet in which transparent materials are arranged in the form of a matrix longitudinally and transversely, light source device arranged in the housing at one side of the support frame, projecting lens device arranged at the other side of the support frame, the support frame being mounted on the housing for a reciprocating movement in a first direction, the support frame being provided with guide rails for movably carrying the file sheet in a second direction perpendicular to the first direction. The projector further comprises retaining device for retaining the file sheet onto the carrying surface. The retaining device is mounted on the support frame for slidable or rotatable movement relative to the file sheet so that the transparent material can be easily changed in the file sheet without focus readjustment.