In the present paper authors give a brief account of a computer program controlled dye-laser spectrometer with spectral range from 400 nm to 700 nm. The Doppler-free isotope shifts in the optical transitions at 432 nm, 436 nm, and 557 nm have been measured by means of the spectrometer. The results tested by the King s diagram are found to be satisfactory. From the measured values of the, isotope shifts the changes in the nuclear mean square charge radii δ for stable Kr isotope are calculated.