Video encoder/decoder with scrambling functions

In a compression coding device having a scrambling function, a variable length coder (220) outputs coded image data. When the image data are to be written to a memory (222a) included in a multiplexer (222), a controller (242) generates a control signal for writing the image data in the order of the positions of slices constituting a single picture, and feeds it to the memory (222a). When the image data should be scrambled on the basis of a preselected scrambling system, the controller (242) outputs a control signal for reading the image data out of the memory (222a) in a different order with respect to the positions of slices, and feeds it to the memory. The multiplexer (222) multiplexes the image data in a preselected position of an MPEG (Moving Picture Experts Group) 2 output data format. Further, the controller (242) outputs information representative of the positions of the slices occurred before and after the scrambling, and causes the multiplexer (222) to multiplex them in another preselected position of the MPEG2 output data format. An expansion reproducing device having a descrambling function is also disclosed.