In amplitude-modulation-type electroholography,the binary-weighted computer-generated hologram[BW-CGH]facilitates the gradation-expressible reconstruction of three-dimensional[3D]objects.To realize real-time gradation-expressible elec-troholography,we propose an efficient and high-speed method for calculating bit planes consisting of BW-CGHs.The pro-posed method is implemented on a multiple graphics processing unit[GPU]cluster system comprising 13 GPUs.The proposed BW-CGH method realizes eight-gradation-expressible electroholography at approximately the same calculation speed as that of conventional electroholography based on binary computer-generated holograms.Consequently,we were able to successfully reconstruct a real-time electroholographic 3D video comprising approximately 180,000 points expressed in eight gradations at 30 frames per second.