Polymer electrolyte fuel cell (PEFC) are expected to be a next-generation high-efficiency energy conversion device, but the catalyst layer structure and formation process have not yet been sufficiently clarified. To investigate the Nafion film (Ionomer) formation process, an apparatus for Surface Plasmon Resonance imaging (SPR) was developed. Using the apparatus, we succeeded in observing drying process of a water droplet with an incident angle of 43.6°, where the observed images correspond to the SPR curves calculated using reported optical constants. Further, we presented that the appropriate angle of incidence for observing the Nafion film formation process is 71.5°.