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Bulk charge accumulation in insulating materials under electron beam irradiation in vacuum environment was observed using newly developed measurement system. Recently, some accidents in spacecraft due to the charging up of the electric potential have been reported. Some of them seem to be caused by discharge due to the charge accumulation in bulk of insulating materials at relatively higher altitude environment. However, there had been no useful method to measure the bulk charge in materials. On the other hand, we had developed the bulk charge measurement system for the polymeric insulation materials used in the power cable. Therefore, we have applied this system to the insulating materials used in spacecraft. Using the improved system, we have measured the bulk charge distributions in about Kapton® and PTFE films under electron beam irradiation in vacuum condition. It was found that the amount of accumulated charge in PTFE was much larger than that in Kapton®.