To provide a data transmission system for transmitting video data at a high bit rate through a radio transmission path, and especially for transmitting video data whose resolution is the optimal to a plurality of output means whose resolutions are different.

This data transmission system is provided with a content providing means for storing video data having predetermined resolution, server equipment to which video data are provided from the content providing means, a plurality of client equipment communicatively connected through a transmission path to the server equipment and an output means installed as a pair with each of the plurality of client equipment. The server equipment is provided with a resolution converting means for simultaneously converting the resolution of video data into two or more predetermined resolutions and a resolution control means for controlling the resolution converting means. The resolution control means controls the resolution converting means based on the resolution of the output means which has requested the video data.