The invention relates to a semiconductor exposing system for projecting a pattern of a mask onto a semiconductor wafer and, more particularly, to such a system having an apparatus for correcting an influence on the resolution by a fluctuation in wavelength of a laser light source. The system of the invention comprises: a laser light source; an optical projecting system for projecting a laser beam emitted from the laser light source onto the semiconductor wafer through the mask; and an apparatus for receiving a part of the laser beam emitted from the laser light source, for detecting the wavelength fluctuation, and for correcting the position and magnification of the optical projecting system in accordance with the wavelength fluctuation value or an apparatus for correcting the refractive index of the optical projecting system.