Abstract: An optical system of an optical information recording/reproducing apparatus including a light source for emitting a generally parallel luminous flux; an objective optical system for converging the luminous flux emitted from said light source portion a medium; a beam splitter for splitting the luminous flux reflected by said medium from a light path directed to the light source portion and guiding the same to a light receiving system; a chromatic aberration correcting element having almost no power disposed between said objective lens and said beam splitter and adapted to correct a chromatic aberration of said objective lens; and means for independently actuating said objective lens at least in an optical axis direction thereof.