Kelvin probe force microscopy (KFM), which has been a common method for studying electrical properties of nanometer-scale structures, is a dynamic-mode atomic force microscopy (AFM) technique combined with a traditional Kelvin probe method used for measuring macroscopic contact potential differences. It allows us to map electron affinity or work function on a nanometer scale. In this article KFM using a frequency modulation detection method (FM-KFM) is first explained briefly. The frequency modulation method plays an essential role in high-sensitive interaction force detection. We also describe applications of FM-KFM to the nanometer-scale surface potential investigations of organic materials including phase-separated self-assembled monolayer films (PS-SAM films) and single polymer crystal surfaces. Furthermore, recent results on the local surface potential study of carbon nanotube field effect transistors using FM-KFM is presented.