The authors are developing an in situ analyzer of field-emission devices that is based on the Seppen-Katamuki (SK) analysis, and they report preliminary results as proof of concept. One of the major differences in the present system from the conventional system is that field-emission characteristics are measured under modulation of emitter voltage. This enables to generate a SK plot, which requires the intercept and slope of the Fowler-Nordheim plot. Field-emission microscope images are acquired by a charge-coupled device camera. The field-emission characteristics of a tungsten-needle emitter were acquired and the SK plots were generated. They found that the fluctuation of field-emission current analyzed by the present system was expressed by motion along a linear line in the SK chart. The above result agrees with those obtained by previous studies.