Furan-resin-derived carbon structures have attracted interest as a component in carbon based composite materials. We have investigated the microstructures of furan-resin-derived carbon by transmission electron microscopy after high-temperature heat treatments. We observed that graphitization occurred at the surface even although furan-resin-derived carbon is believed to be a non-graphitizable carbon. On the other hand the interior of the specimens exhibited a cage-like structure. Specimens heat-treated at higher temperatures exhibited a well-developed cage structure, as evidenced by the number of stacked layers and their periodicity. Post-column type EELS was utilized to study the chemical state of the interior of the specimens. All of the EELS spectra had a characteristic edge structure showing the existence of π bonding. There were not significant differences between the spectra of early-stage and well-developed cage structures.