To provide an image data communication system capable of reducing delay time between an analog-to-digital conversion process and an image compression process, and a delay time between an image expansion process and a digital-to-analog conversion process.

A first communication station 2a for transmitting image signals has a video ADC(analog-to-digital converter) 4 for digitizing analog image data, an image compression device 6 for image-compressing the digitized image data in the odd lines and in the even lines independently, and a communication IC 8 for outputting the compressed image data in the odd lines and in the even lines to a signal transmission path 3. Also, a second communication station 2b for receiving the image signals has a communication IC 11 for receiving the image data in the odd lines and in the even lines which are outputted to the path 3, an image expansion device 13 for expanding the image data in the odd lines and in the even lines, and a video DAC(digital-to-analog converter) 15 for converting the expanded imaged data in the odd lines and in the even lines into analog and combining each of image data to restore it to the original image data.