Disclosed is a projection lens system for use in an optical system for magnifying and projecting original images displayed on plural image display devices onto a screen through projection lenses provided in corresponding relation to the image display devices, which projection lens system comprises plural lens elements and in which according to colors or degrees of fineness of original images, the number of constituent lenses, or the shape of lens surface, or an effective aperture of at least one constituent lens element surface, or the number of constituent lenses and the shape of lens surface, or the number of constituent lenses and an effective aperture of at least one constituent lens element surface, or the shape of lens surface and an effective aperture of at least one constituent lens element surface, or the number of constituent lenses, the shape of lens surface and an effective aperture of at least one constituent lens element surface, are changed at a time.