To provide a data transmission method and a data transmission system that adopt a system, where a plurality of composite 8-bit word stream data generated on the basis of a plurality of 8-bit word stream data obtained by dividing word stream data and each including word synchronous data is subjected to 8B/10B conversion and S/P conversion and the resulting data are transmitted, and use a plurality of transmission channels to transmit digital video signal data.

A plurality of composite 8-bit word stream data is formed by inserting an attached word data group including 8-bit word synchronous data having a preset code to each of a plurality of division 8-bit word stream data obtained by dividing the word stream data consisting of consecutive word data each in a prescribed bit number, a P/S conversion means incorporating an 8B/10B conversion means applies 8B/10B conversion to each of a plurality of the composite 8-bit word stream data and the P/S conversion means applies P/S conversion to each of a plurality of the composite 8-bit word stream data to obtain a plurality of serial data, each of which is transmitted.