1-dimensional (1-D) nanocarbon materials such as carbon nanotubes  (CNTs) and carbon nanofibers (CNFs) are quite promising as electron emission sources in the near future. These 1-D nanocarbon materials possess very high aspect ratio, thus readily allowing to emit electrons under relatively low applied electric fields even at low vacuum pressures. During the field emission (FE) process, degradation in current and structural damages of the nanocarbon emitters often occurs. Regarding these phenomena, for the practical use it is essential to fully understand the fundamental physics underlying the FE process particularly for individual nanocarbon emitters. In this paper, we are challenging to study the structural change of individual ion-induced CNF by electron current flow during FE process, using in situ transmission electron microscopy (TEM) facilities.