Distribution of the mechanical properties of Langmuir films of myristic and stearic acids under the transition from gas to condensed phase was observed by measuring local propagation of thermally excited surface waves (ripplon). Ripplon light scattering system was improved so that the laser beam could be scanned over the surface. Inhomogeneous structure was successfully observed with a spatial resolution of millimeters, in which a stiff film with high surface elasticity and a region with nearly zero surface elasticity coexist and separate into two single domains. The surface elasticity and the area of the stiff phase were qualitatively examined to confirm that the macroscopic droplet observed was a homogeneous liquid film. Fine structure of the boundary between gas and condensed phases was also observed with higher spatial resolution of 100 mum by measuring the propagation of high-frequency ripplon.