A simple system of CARS (Coherent AntiSTOKES RAMAN Spectroscopy) was constructed and applied to measurements of the distribution of the concentration of hydrogen in a hydrogenair diffusion flame. The apparatus is similar to that used by TARAN et al.: The incident beam from a giant pulse ruby laser into a cell filled with high pressure hydrogen generates stimulated RAMAN emissions. The first order STOKES light selected from the emissions together with the original ruby laser light is focused in the system containing hydrogen and the intensity of CARS light thus generated is measured. Using the method similar to that for estimating the density distribution of a axially symmetric system from a shadowgraph, the distribution of hydrogen concentration in the flame could be determined quantitatively. The results were compared with that of the calculation using the BURKE-SCHUMANN's model and the problems which should be considered in experiments with this technique were discussed.