a light source for an endoscope is disclosed for illuminating a subject , the image from the subject being received through a leading end of the endoscope , and being projected by an objective lens onto a solid state imaging device . light from a light source lamp is projected onto the subject sequentially with the light transmitted through three color transmitting filters . a reflector is provided to reflect light from the light source lamp in a parallel light beam . a convex lens system for converging the parallel light from the reflector . light from said source lamp is transmitted through a light guide to the subject . a first and second lens systems are positioned between the input end of the light guide and the convex lens system for converging the light onto the input end of the light guide . the light guide is disposed within an insert member of said endoscope . the lens systems reduce the sectional area of the light beam and restrict the included angle of the light beam . a rotary color filter is provided in said light beam and includes interference filters having high heat resistance for passing light of only a specific wavelength , to provide different colors of illuminating light to the subject .