We have developed a current flow analysis system for Field Effect Transistors (FET) using a conductive cantilever of a probe microscope. Using this analysis system, nanoscale current images were observed on a pentacene active layer grown on a bottom electrode in ordinary FETs. When gold (Au) was employed as a bottom electrode, we found the special region around the electrode edge. The current flow hardly occurred in this region. On the other hand, using a conductive polymer (PEDOT) bottom electrode, such a region was not observed. From the detailed observation around the electrode edge, we concluded that the special region would be caused by diffusion of Au particles that evoked heterogeneous pentacene growth, and then the heterogeneity worked as a contact resistance.